That's a good plan.
You need an 5.0L engine with the AOD (not AOD-E) out of a Mustang between about '87 and '94. You could probably go back as far as '83 in the Mustang and still get the HO motor, dunno about the AOD. Of course the farther back you go the engines and trannys will be in worse condition. The Lincoln Mark series and T-Bird/Cougar series are also potential donors as loong as they have the HO motor.
I don't recall if the AOD-E starts after the end of 5.0L production or not, but they will require a computer to run.
You'll need to swap oilpan, oil pickup, front timing cover, fuel pump ecentric, fuel pump, intake, distributor, and exhaust manifolds from your 302 to the 5.0L.
Due to the roller cam and higher compression, the later 5.0L engines should out-perform a mild 302 even after swapping out the FI for a carb, so its a win-win situation.