IF (and that's a big "if") rust is not a problem, there's nothing unusual about a GT6 restoration. It's rare to find an unrestored GT6 without rust. In fact, I'd be sceptical of any unrestored GT6 whose owner alleges that it has none. Check for rust in all the usual places (i.e., pans; sills; A-post; bonnet; rear valence; roof above/along the windscreen, etc., etc.).
The GT6 shares many body, electric and suspension parts with Spitfires and parts are easy to source and relatively inexpensive. Engine bits are not hard to find, either. The gearbox is robust and not hard to restore, also with reliable parts vendors and good aftermarket support.
In the rear suspension, depending on the model you'll either have a swing axle or rotoflex couplings. If it's a rotoflex, look for cracks and anomalies in the rubber doughnuts, and of course the usual suspension wear items in either version. Check spring and suspension mounting points carefully for rust and strength. Test drive the car on a bumpy road and listen for clunks, plunks, whines (diff problems?) and vibration.
Also, make sure the frame is straight. This is a biggie since it's expensive to straighten or repair a bent frame. Seems that most GT6s were driven hard in their day and often suffer collision damage, sometimes not easy to find.
Often the damage was to the front end: open the bonnet and look at the spacing shims in the front suspension where it attaches to the frame: if the shims are unusually unequal (lots on one side, few or none on the other), you might have a bent frame. Also, measure tire clearance in both front wing wells. Clearances between the tire and the wheel well/bonnet should be the same on both sides. Check body panel gaps for consistency, too, which can be a sign of frame weakness/damage. Further scrutiny of the frame is a very good idea. Get the car up in the air and take measurements for trueness from front to rear, and visually inspect the frame (with lots of light!) for rot and anomalies.
No rust, straight frame: you're good to go for a project car. Nice examples of GT6s, especially MKIIs, are so rare that most of us are compelled to look for good project cars instead of nicely sorted ones. IF you can do most of the work yourself, a GT6 is one of the least expensive LBCs to restore, IMHO. If you're lucky, you might just be able to restore it and spend close to the market value of the car (did I say "lucky"?
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And I must add that well-sorted GT6 is a thrill to drive. Plenty of power (130HP is easily coaxed from the 2000 using period-correct parts) and it handles very well. And the hellish howl of that silky smooth six is a big part of the joy of owning a GT6.
I wish you luck, always good to see someone rescue one of these rare and beautiful Triumphs.
Let us know what you do, POST PHOTOS, and good luck! :thumbsup: