it looks like a great project.
I personally would buy a 944 or 951, because I love the body style, and the 85.5+'s still have the updated beautiful interior and the 951's can be fast with excellent handling, I mean it can compete with the 240z with the same type of suspension mods. And Lt1s fit under the hood nicely for about the same price as the Z, but I would get an N/A model if you were up for the conversion, it also doesn't affect the 50/50 weight distribution in them.
When I had mine, I met a guy who did the Lt1 conversion with the stock 951 trans, the car was retardedly fast at auto-x. It was also running low 12s high 11's. It had a 0-60 in well under 4 seconds as well, like 3.3 with alot of traction issues.