[66Submarine]

Nice truck. As everyone else said, the engine seems like a normal 283 (or maybe one of the weaker variants of 327).

"1970 3.73 positraction if I can find a center unit"

Not sure what you mean by that?

Swapping to 4.10's from 5.14's will make your current engine speed at 50MPH occur at 63MPH or so. You might also consider using a later 14 bolt (1973 and later) rear end.

Make sure you don't go too tall and end up lacking power to go up hills in high gear. I personally wouldn't go taller than 4.10...even that isn't giving a 283 all that much leverage if you're trying to haul something and keep up with traffic IMO.