55.2-59 59 GMC 270-336 swap.

[dsraven]

if you're doing a numbers match truck, then, hey, do what you gotta do. if doing what needs to be done to get it going and running so you can drive it, then, hey, for me, an ls swap is the answer. easy start, good fuel economy, pretty easy to find a donor truck with everything you need, no carb issues, etc etc. it is the new small block replacement. back in the day everybody was swapping a sbc into the spot where the old tired engine lived. nowadays it's the ls engine. keep the old stuff and don't torch things apart so you can still go back to stock. oil up the parts and keep the old stuff on a pallet in case you wanna sell it someday. it can be put back to stock if wanted, on somebody else's tab. but today, with the fuel prices like they are, and the parts hard to find, a fuel injected engine and ccomputer controlled trans from a late model donor is the way I would go. thats just me, if you wanna do the old truck thing then that is you. your call. a numbers match truck is gonna be expensive because they look at everything. a half done numbers match doesn't really make the mark from the numbers match perspective so, what the heck. do what is gonna work for you, keep all the old parts. doesn't seem like using a really old "good running engine" is the most economical way to go since it may give out on you at any time.
this is just my opinion. it is your truck and your pocket book. you do what you want to do. just giving my 2 cents. think about it, if a buddy of yours showed up with an old truck and he said "yeah, it is all stock except the driveline because it is so expensive to do an old engine so I installed a 5.3 LS engine and an automatic trans from a late model truck in there and I kept all the original stuff on a pallet". would you fault him? he is driving it and having fun, right?