[Mike C]

I prefer the manual trans for any sort of “work”. The manual trans lowers rpm on highway about 5-8 % because of converter slippage compared to the auto. Go from 32” tire to 33” tire and you have effectively lowered your cruise RPM, then build that 496. I’d run a cam in the 218 deg at .050 range on a motor that big if not a little bigger.

I have a ‘71 GMC 1/2 ton factory 402 that I’m pretty sure the exhaust from the manifolds is 2 1/2”. Regardless of what is factory or not, I’d run dual 2 1/2” pipes and the Walker DynoMax 20” case turbo mufflers.

The Sanderson manifolds are nice but REALLY pricey.