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An '85 would be either a 300, 351w,460, or oil burner, right?
If so, the next question is what kind of clutch do you have? Methinks you should have a hydraulic clutch already.
If so, you can use the Ford-installed ZF 5 speed. These use an integral bell, so you MUST get one from the same engine series. Clutch is hydraulic, internal for the 300-351w, external for BB and OB.
Another alternative which bolts to your existing bell, uses your existing clutch but requires an adaptor, is the NV4500.
Mazda 5 speeds from F150s would be an alternative if you don't tow or haul max loads. These are 300/351w pattern only, integral bell, hydraulic clutch.