Hmm, I'm surprised an 89 3500 crew cab would come with a 350 for an engine.
Swapping to a bigblock is a pretty big chore if you don't have a donor truck to start with. Every bracket and accessory is different, that's not even getting into all the computer controls and tuning differences.
My old 79 is a factory 454 1 ton, so it was already there, when it was time for a refresh the 496 stroker just seemed like the next logical step for me
If I were in your shoes and didn't have a donor truck to steal from, I'd stick with the small block package and maybe look at some of the crate engines like the HT383. Or if you know of a reputable machine shop then stroking the 350 to a 383 is cost effective. Actually it's about a wash when it comes to rebuilding one anyway. That's probably the least expensive way to go if you dont' mind some down time.