stepside engine suggestions

[lifted k10]

Hey guys, my 86 2wd stepside 4.3 with a sm465 finally blew the motor after 312,000 miles. Safe to say I think I got my money worth out of the truck. LOL. I have a low mileage rebuilt oldsmobile 455 with a mild cam sitting in my garage, should I put that in her with the sm465 and with the money to buy a crate engine and rebuild the rearend with some gears and a posi or buy a crate motor 350, or ls engine. Let me hear ur thought's or suggestions.