Are the exterior parts of a 1979 GMC k2500 pickup compatable with that of a 1981 GMC k1500, as far as doors, glass, and trim.
Yes sir, body wise pretty much everything interchanges on these trucks and most chassis parts interchange with the exception of 2wd/4wd parts. The front clip will change over also you just need to swap out the wiper components and core support bushings I believe, but keep the old round eye style if you can. The 73-80 aluminum side trim wont work on the later front fenders but you could always put on new 80-87 stick on trim on the older body if you really wanted to. Most interior parts will swap over too.
Pretty Much Yes They moved around bolt and screw holes a little bit so in you're junkyarding , look really closely before paying , I had to look hard to find the internal release hood latch for my '76 as they changed the header a few years after it was built Dashboard binnacles too change a bit , wiper switch mounting and little (but maddening) details like that . DO post what you're doing and ask lotsa questions as the good folks here have done it all and will have great tips .