i just bought an 86 pickup cab that i am going to put on an 79 motor home frame, i should have posed here first to make sure everything will work. i have an 79 motor home that the motor home part is all rotted out. I am going to make an flat bed truck. im going to run the motor home 20r motor and 4 speed trans.

 

You will have to either move the cab mounts or make new ones to mount the later model cab to the early model frame, other than that you should be able to make it all work.

 

i'd reccomend taking a close look at the wiring harness, alternator, especially igniter and coil assembly and make sure that the one in your new cab specifies to run the 20R.
I just went through the same ordeal putting a 82 cab on my 79 20R 4spd chassy, and ended up having to swap in a 22R to match my harness, acessories etc..
a lot of small elec. i have found are pretty year specific to make a motor run in a different cab..as far as an 86, i would check if its EFI, extended cab, powersteer etc to make sure the swap would go properly and easily..

 

86 should have an 22r not an 22re correct?

how much differnt are the cab mounts

 

86 could have either 22r or 22re both were available.

 

and the harnesses were completely different too, and the gas tanks, and a bunch of other random stuff