Wiring harness is different, so I'm using the '83. Oddly, R & L taillamp wiring uses the same colors in the '83 FSM, but the truck has dark or light green wires. The FSM is wrong there, I guess.
Fuel tank switch & some plumbing differs, using '83 switch and re-routing hose to use lt-side '79 canister vent hardline ('83 is on rt rail).
Using the bigger '83 air cleaner for its fresh air duct the '79 lacks.
Looks like the '83 cab mounts are mandatory, as advised on this board, thanks for that info! ('79 mounts differ quite a bit in height, apparently due to cab brackets.)
Will try to use the '79 radiator (thicker core in my case, and in xlnt condition) with the '83 rad support.
My '79 K cab had the bolt-in floor hump, cut the '83 C cab floor out at the crease provided (thanks to some unsung GM engineer!) and it fell into place. Had to cut some of the floor to the rear of the hump out & swap into the "new" cab. No big deal, I run a body shop.
Sprayed bedliner material on the floor and kick panels and lower rear panel. There will be no rust.
Spray-foamed the gap between inner & outer roof; the '83 roof was surprisingly flimsy. The foam fixed that and will quiet my poverty (no headliner, base trim) ceiling.
Running the floor wiring either through the T-case lever boot or through holes at the firewall & rear "shelf" floor and through the rockers, so no wires on the floor.
Had to swap the '79 4-LOCK lamp, harness & lens into the '83 cluster. No problem except trimming the retainer clip for + power at the fuse block. Ground lugs the same.
More work than I expected, but coming along and a good brain exercise.
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