as a heads up, some guys put the rad in front of the rad support to gain a little room.
is the '64 rear suspension not a trailing arm suspension? my '63 gmc was trailing arm with coil springs. pretty good ride, no wheel hop to speak of if doing a burn out (well, as much of a burn out as you can with a stock 283, haha). coil springs maybe have less weight carrying ability. I installed variable rate springs for a good ride with no load but able to carry some weight once the soft part of the springs was overcome. I guess that doesn't matter too much since you would cut all the brackets off anyway, or swap in the whole rear suspension for an added bonus of a lot more work. lol.
here is an rpm calculator if you wanna find out what you rpm will be on the highway or any given trans gear
https://spicerparts.com/calculators/...rpm-calculator
and another
https://www.randysworldwide.com/calc...sion-ratio-rpm
and a last one
https://www.tremec.com/calculadora.php