That sounds like a reasonable idea, Doug -- I just get worried whenever friends talk about going racing cheaply. Those too words (racing, cheaply) are mutually exclusive in almost all cases.
Wikipedia has some info on Mustangs, not a bad place to start (With appropriate grains of salt, of course):
https://en.wikipedia.org/wiki/Ford_Mustang_(third_generation)
https://en.wikipedia.org/wiki/Ford_Mustang_(fourth_generation)
I'm a big fan of the Fox-bodied (79-93) Mustangs as a value fun car. Had a girlfriend years ago with a '92 GT that her ex had done all sorts of performance work to. A very quick car. They can be found pretty cheaply, and there's lots of performance parts for the 5.0 V8.