I've got a 1974 GMC Sprint project car. It was originally a 350 small-block Chevy with a TH350 trans, but I sold the engine and trans and installed a 454 [big-block] and TH400 trans in it.
Keeping older vehicles running is more popular now than at perhaps any time in recent history. New hardware, wiring harnesses, ECUs, turnkey crate engines, and accessories make 4x4 repowering easier ...