'65 5.0 efi no start problem

I would start by removing the distributor to make sure all of the teeth on the gear aren't chewed up. Just make a mark with chalk or a sharpie between the block and distributor of where the timing is set. If all is good there reinstall the distributor and check the timing. I know with the EFI the computer controls the timing based on driving style so if the previous owner manually messed with the timing that might be why you're thrown off.

This just made me think of another possibility could be that the distributor has been turned and the timing is way off. That's actually the most likely thing. Just google what you should set your timing at and re-time the engine.

We have very similar cars. I've got a 95 motor in my 65 convertible. I did the swap myself though.

Step one is to pull codes from the computer. There will be threads in the 5.0 Fox section on how to do this. This step may not tell you the problem, but it will let you know what is NOT the problem. For example, if your TPS (often a problem, but unlikely in your situation) shows no faults, then you don't have to mess with that.

Buy a REAL shop manual for the 1995 Mustang. This is filled with very valuable info about your motor and will help you narrow down the possiblities. During my install/troubleshooting it was never far from me.