If you are on a budget take a look at 83-97 thunderbirds. the 83-88 are on the fox platform and have parts commonailty with alot of the mustang aftermarket. The thunderbirds dont have the mustang name on them and will be 500-1000 cheaper than a mustang in the same condition. That money savings could be the difference between a questionable builder and a quality builder.
The biggest downside to thunderbirds is the very limited selection of manual tranny cars. There were some turbo and super coupes built with T-5s. A T-5 can definatly be installed in a t-bird its just more of an adventure.