Ford Repair: comp.change 1987 F-150 4x4 4.9 to a 5.0, rearend ratio, speed density

Question
Jordan...I'm converting a 1987 F-150 with a 4.9 liter, 4spdod tranny 4x4; to a 5.0 liter, 5spd mazda tranny. It also has the 1345 transfer case. I'm replacing that with a 1356. My question is; witch computer do I get? My ford man says there are 5-6 different ones. Does the rearend ratio make a difference? The truck is a XL package truck, but I'm replacing the cab with an XLT rust free cab.I have most of the parts I'll need, but i'm stuck on the computer part, can you help???

Answer
your EFI computer should be the same model as from the car you took the engine from.  There are all pretty much the same.  The induction is the important part, there are throtle body injected computers, Speed density computers, and MAS Air computers.  If you need details on how to find out what style motor yours is, ask me again.  Im not sure what 5 speed mazda transmission your talking about, but im guessing its what comes in late model trucks.  The rear end ratio makes no difference except to your speedometer which can be adjusted by changing the gears on the cable.  You only have to worry about rear ends when you come to the newest cars with electronicly controled transmissions, some 1997, 98, 99, and after.  Keep in mind that you may run into more problems than you expect.  I know that the k member for a six cylinder mustang is much different for the straight six motor compared to the 5.0.  In short, you may have to replace a lot of other parts.  Its best to have a junked out v8 f-150 somewhat like yours to use for parts in case you need them.