Okay forget that Hemi head question. I think what I'll do is take a 318 poly motor and put a 360 crank and pistons in it. And do a little bit of Port work and bigger valves to the poly heads an a little more cam and try to find a four Barrel or two four barrel manifold for it.
The poly motor is a torque monster so imagine it could move that truck.
That's if I can't get my Hemi from rrr.