The engine itself will usually either be a 289/ 302 / 5.0L-looking smallblock (so a lot of kits are potential donors), or the big-block pushrod FE (in which case the Revell parts pack Ford 427 works). The gearbox is a little tricky, as the cars were built with Colotti, ZF and Hewland transaxles. If you want to be accurate, it helps to know which particular car you're building. Cobra kits are also good engine sources.
The AMT MkII ( kit # T 232-200) comes with a 255 / 289 bottom end (with gearbox) that can be built as an OHC or a pushrod, complete with the bundle-of-snakes exhaust, AND a pushrod big-block 427 (with gearbox)
MPC MkIV (kit #1-0561) has a big-block pushrod engine and transaxle.
Revell / Monogram (originally Aurora, I think) Ford GT (kit #0565) also has engine, exhaust, gearbox and suspension, though the proportions are not the best.
Though the virgin kits can be pricey sometimes, you can often find gluebombs with everything you need.
Edited by Ace-Garageguy, 19 March 2013 - 12:00 PM.