'81 302 f150 to '81 fourcylinder pony?
 

I just got my hands on a '81 mustang four-banger and want to know if it is compatible with a '81 F150 302cid, and
what would I need to change?

This sounds like a lot of work for not much power. The '81 truck engine only had about 135 hp. Motor mounts, exhaust system, transmission and mount, ignition module, springs, and probably 50 more things I didn't think of. Also the front sway bar on a 4 hole Mustang is too small to handle a V8 and they don't have a rear sway bar. Your 7.5 rear can handle the power of a stock '81 302.

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E-cam, pullies, 3.27, Mac Off-road, 2 chamber Flowmasters, 5 lug conversion

Does not sound like a good swap idea.

Sky