Hi Larry,
Good luck acquiring that TR4!
I must admint I'm a bit biased toward TR4, perhaps because I've owned the same one for about 30 years.
The commission number of the car is your best source of information and you can get even more from the British Motor Heritage website (
https://www.heritage-motor-centre.co.uk/archive/certificate.html), by purchasing a certificate with details about the original build of the car, if you wish. That will tell you what equipment was originally supplied and how the car was finished, and usually has engine number at least, if originality is a concern. But, Triumphs did not have matching numbers for engine/body/commission/etc., like some manufacturers did. Commission number will be CTxxxxxxL(O). This might be prefixed with STC/year on a title or registration. The "L" at the end indicates LH drive/US version. If there is an "O", too, that indicates the car left the factory with an overdrive installed.
Back in the days when it was sold, TR4 were not given a model year like they are today. They were registered the year they were sold. For example, my TR4 was built in 1962, but is registered a 1964.
There were a number of subtle changes - and a few not-so-subtle - to the TR4/4A over the production run from 1961 to 1966 ('67/68 if you include TR250/5 which have the same basic body/chassis, but the 6-cyl. engine same as TR6).
Some of the production changes might be considered improvements - or not - depending upon your tastes and what you are looking for in the car. One purely cosmetic example: Personally I like the TR4A grill better and have used one on my TR4 (but presently have the original re-installed and am thinking of leaving it for originality's sake).
Earlier TR4 had a rather utilitarian looking white-painted dash (which I really like), while a fancier wood dash was an option. Later TR4 and TR4A increasingly had wood-covered dashes. AFAIK, by the time of TR250/5, all were fitted with wood dashes. Interiors were mostly finished in vinyl, but some cars had leather-faced seats.
The interior of the TR4A became a little more refined in a number of small ways. Minor changes to the cylinder head and stock exhaust manifold slightly improved TR4A performance. To make it a little easier to use, the clutch was changed on TR4A, to a slightly smaller and now more widely available diapraghm style. This is generally reliable on TR4A, but became problematic when used in combination with some other changes on the later 6-cyl. cars. The TR4 clutch has heavier pedal pressure, and weighs a lot more overall, but is generally a "bullet-proof" setup!
TR4 have a "ladder frame" that's stiffer and stronger than the TR4A and later cars. TR4 frame was essentially inherited from TR3, but given a wider track, beefed up in a few areas, and adapted for rack & pinion steering, which was an added feature of TR4 and later TRs. The frame is also a little less prone to rust than the later cars, but still can be a problem (should have been taken care of by the shop you reference, I would hope). I think part of the reason a friend of mine discovered when he cut up some frames a few years ago. TR4 (and earlier) frame rails appeared to have been painted *inside* before assembly (tack welding that leaves most paint intact). Later frames appear not to have been painted inside, plus have more openings for water and exhaust to intrude, and might be made of slightly lighter steel.
TR4 have non-adjustable front suspension geometry, meaning both caster and camber are fixed (but there are ways to adjust both, if needed, just not very easily).
The later cars have shim-adjustable front suspension. However, this is a weak point and reinforcement of the mounts is always highly recommended. Late TR6 finally got a beefed up inner/lower suspension mount. So, the front suspension was improved in some respects, but was also weaker.
The new independent rear suspension (IRS) introduced with the TR4A gave a nicer ride, but is a lot more complex and has some weaknesses, too. In fact, an estimated 25% of TR4A were still produced with a solid axle, similar to TR4, at the request of U.S. dealers who were concerned the new setup would be "too un-sports-car-like" for buyers! Even the solid axle version of the TR4A use the same frame as the IRS versions, however, so don't enjoy the stronger/stiffer ladder frame of the TR4.
The solid axle TR4/TR4A is generally easier and cheaper to set up for racing, where Triumphs were having a lot of success both in the U.S. and in Europe. On the other hand, the IRS could be very competitive, in some ways better on the track than the solid axle. It just required more time and money to dial in properly.
The rack & pinion on later TR4, TR4A and all the way through TR6 is different from early TR4. Many owners of the later cars remove the rubber rack mounts and replace them with aluminum ones more similar to the early cars!
Changes to steering and suspension helped to reduce bump steer tendencies and were probably also to better accomodate emerging radial tire technology. But, the prime concerns probably came from the marketing dept. and a softer ride was the general trend, to best appeal to the huge U.S. market (about 90% of TR4/4A sales).
The IRS cars - TR4A and later - never saw factory European rallying like the earlier cars did, due to concerns about the flexier frame and weaker suspension. But, in the U.S., the IRS cars were raced with factory support, and saw a lot of success in many events, including the Sebring 12 Hour endurance race.
As already noted, SU H6 carbs (also ala TR3) gave way to Zenith Strombergs, but eventually returned to SU HS6 carbs, then back to ZS! They really are pretty equal in performance, the later SUs are probably easier to get parts for and SUs in general are a little easier to tune up at home.
You mentioned that the car you are looking at has a hard top, and I agree that an original one is a valuable addition, adding probably $2000 to the value of the car. There were aftermarket tops too, though, that don't add as much value. Some were fiberglass, both one and two-piece designs. One had an injection molded black plastic roof panel combined with a fiberglass window frame (sometimes called a "Sebring" top). Nearly all have Lexan or some other type of plastic windows. Original tops have a cast aluminum rear frame and the hard, roof panel is either aluminum (early version, first 500 made) or steel (later version). Original tops came with Triplex glass windows, but these were sometimes changed to plastic by racers to reduce car weight a little. Non-original two-piece hard tops add value, but probably only about half that of an original. One-piece aftermarket tops probably only add $200-400 value, and some styles actually detract from the car's appearance, IMHO.
The two-piece hard top is often now referred to as a "Surrey", but that's not the original terminology. Triumph simply referred to it as the "Hard Top", which included the rear window & frame, and the metal roof panel. These were fitted at the factory, or available through dealers as an accessory kit that included all the trim and hardware. To fit a kit, the cockpit mouldings were removed, different interior trim panels are used in the back, the "hoodsticks" are removed, and TR4 are fitted with special, longer stainless steel fender beading (later used on all TR4A) and longer rubber & fuzzy weather stripping/seals.
In Triumph catalogs, the "Surrey" was just the vinyl panel and it's small folding frame, that were a separately available accessory for the Hard Top. These were offered simply because the hard top roof panel is too large to stow anywhere in the car. The Surrey was useful for anyone who got caught in a rain shower after leaving the roof panel at home for a little open-air driving!
The TR4 two-piece hard top is often called the first "Targa top", and essentially was copied by Porsche for the 911 Targa five years later.
Another highly desirable optional accessory for TR4/4A is an A-type overdrive. To find out if the car you are considering has one, look for an overdrive switch on the RH side of the steering column. It will be a lever like the turn signal on the LH side. If the body is off the chassis or the gearbox cover is removed, or looking up from underneath, you can see the overdrive itself mounted on the rear of the gearbox. There is some additional wiring also. A good, working overdrive probably adds $2000 to the value of the car, and gives an effective 7-speed gearbox since it works on 2nd, 3rd and 4th gears. Some folks like the later J-type (TR6), which operates more gently, but personally I think the A-type is much, much stronger and appreciate it's rapid shifting capabilities. Some cars were shipped from the factory with overdrives fitted. Or, conversion kits were provided so that they could be added by dealers.
Let us know if you get the car.
/ubbthreads/images/graemlins/cheers.gif
Hey Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
A friendly reminder - be careful what links you click on here. If a link is posted by someone you don't know, or the URL looks fishy, DON'T CLICK. Spammers sometimes post links that lead to sites that can infect your computer, so be mindful what you click.