Originally posted by Slow-N-Low
If you're replacing a Cleveland motor, then all you have to worry about is the details. Make sure that you re-use the oil pan and oil pump pickup, or make sure the new ones work with that car (and each other). Make sure that you have new motor mounts and other little things beforehand. Contrary to what some have said, you'll have several electrical connections to keep track of, including oil pressure and temperature sensors, starter and electronic ignition.
IIRC, the Mach 1 was a big block car, so you're probably going to need to investigate what's needed for the swap. It might be as simple as using "adaptor" motor mounts, or you might need to track down a new engine cradle. This is true even if you're swapping a 351 Windsor for a 351 Cleveland, BTW. Do the research first, and save a lot of headaches later.
Standard engine with the Mach 1 was the 302 V-8, and all other V-8 were optional, except the 330 hp 351 found on the Boss 351. Optional V-8s were the 240 hp 351 V-8, the 285 hp 351 V-8 and the 370/375 hp 429 V-8. All 351 V-8s were of the Cleveland engine family. In May 1971, a low compression 280hp 351 V-8, called the 351CJ, replaced the 285 hp 351 V-8 that was available at the beginning of the model year.
302 is a small block.
edit: 1971 Mustang was the first car i ever took apart and put back together.