need help with a question about switching cabs

[dhutton]

i have a 1978 Chevy 3/4 truck and the cab is in very bad condition the truck is manual and 4 wheel drive.  If i put a cab off of a 78 4 wheel drive automatic, what would i have to do to make this work.

[Blazin]

Are you swapping the 85 nose as well?
If you are not you will need to make sure the pin positions in the 78 nose wire harness for the engine, and nose body electrical are correct to plug into the 85 bulkhead connector in the fire wall. The 78 plug will fit but stuff might not work correctly because of the pin position being in a different order. If you are leaving the 78 nose you might want to consider welding up the hinge holes in the cowl of the 85 cab.
You will have to cut the center floor hump out, and put the one from the 78 into the 85
You will need to change the winshield wiper stubs as the one on the 85 will stick up to high, first time you close the hood they will get cleaned off.
You will either have to switch you linkage style clutch pedal over to the 85 cab. Or you will have to swap out the bell housing from the 85 so you can run the hydraulic clutch. I personally would switch and run a juice clutch.
You will need to use the 78 cab mount bushings, or new bushings but for the year specific frame.