1983 GMC Sierra rebuild

Stick with a 350 c.i. That was GM's most popular engine for many years. Because of that parts are readily available and inexpensive. It weighs about 100 pounds more than the Chrysler small blocks so in stock form it has a power to weight ratio equivalent to Chrysler's 318 c.i. The added weight is mostly in thicker cylinder walls so where the Chryslers can only be bored .040" maximum oversize, the GM engines can be bored much more if it ever becomes necessary. You'll have no trouble finding standard and high performance parts at any auto parts store or aftermarket suppliers.