My '78 Spridget racer has a '78 Spitfire engine.
The main difference is the oil pan and oil pump pickup. If you forget to swap the oil pump pickup, the oil pressure will drop in turns.
Note that the 1500 and 1275 trans are completely different.
I would think that for a street car, the 1500 is fine.
Be sure to check the crank and *always* put new thrust washers in, even if the old ones look OK. Rod bearings are a weakness too. I swap thrust washers and rod bearing every 25 hours of use.
Jeff's idea of trimming the head is good. You can take off 0.100" easily. But be sure you don't mind running high test gas.
For a street car, you may be best to leave things almost as-is and not go too crazy...9:1 pistons, a crank regrind, very mild (or stock) cam, new timing chain, gaskets....that sort of basic stuff.
These engines will grendade if pushed too hard.
Swapping the single ZS car for a single SU is a nice swap. The twin SU Euro/Canadian is better, but hard to find in the US.
Don't plan on revving this engine too much unless you are planning on a full balance-job and regular bottom-end repairs. Use 6000 RPM as an absolute max, with 5500 max being preferred (for a standard engine).
A header can help if it is a good one....the Pacesetter header is low-quality and not very good (in my view).
A nice touch is using the Spitfire overdrive trans. It can be fitted with some drive-tunnel pounding.
After five years, I'm fitting a 1275 to my car....but I'm keeping the 1500 for my street car.