It should all work without a problem. If the '74 head doesn't have the smog ports at the back, just leave off the smog pump and lines. Everything else should work fine. The only other issue you may have, is the flywheel or flexplate. They cannot be interchanged between the 2 engines. If you're 'stang is an auto, the 28oz flexplate off the '74 engine should work fine. If you have a manual, you're going to need a flywheel that has a 28oz balance and is compatible with the later 10.5" clutch.
Your early cam has a different firing order than the 89 HO engine -
you basically just need to reroute your plug wires.
Also, your efi fires the injectors in that newer firing order so it
will run rough at idle but smoothen out once it gets a few r's up.
Windsor-Fox (I think it was them) had an article about doing
an efi fit onto an older motor. There was something about the
water transfer ports, I think it was, where they were diff size
from the motor to the intake, but being careful they got it to
seal without leaking.
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