It has been a while since I updated, but some serious progress has been made.
So here we go:
The truck came with a 216 in it and I had been debating on keeping it when after a little research I discover the 292 from Chevy. It was exactly what I was looking for, a big sized inline 6, and enough horsepower and torque to have some fun with. I located one in Albany, NY (after a few weeks, a lot harder to find than I originally thought. It had been pulled from a 1970 Chevy farm truck. The guy threw in an additional carb and exhaust manifold, which was great.
So we have a motor and transmission finally (292 with the NV3500).