A 352 will respond to a 4bbl and dual exhausts, either with headers or stock manifolds. An aftermarket aluminum manifold removes a lot of front end weight, the factory manifolds weigh a ton! Don't pass up a cheap one, though, they do work, and the truck is pretty heavy anyway.
If you have a 3 speed stick, a good swap is a four over from a mid-70's pickup. It fits the bellhousing, clutch, and driveshaft you already have, and is a 70% or so OD.