With only 26K miles, that one is barely broken in. I'd strongly suggest keeping it, and doing whatever it takes to get it back into running shape. Unless the engine is seized up, it's highly unlikely it will need anything more than a good tuneup and maybe a carburetor rebuild to put it back into good condition. One of the really oddball features of those engines was the bolt-on cylinder assembly- - - - -worn out cylinders could be removed and replaced instead of boring the block and fitting new pistons, since the cylinders and crankcase were bolted together, not cast as a single piece. Like most other GMC engines, they were built to be reconditioned repeatedly.
Jerry
