318 build #2 "cost minded" for the '74 Duster

318willrun said
Headers help a lot. We don't want headers on this car. It has manifolds and 2.5 duals out the back.

I had one I used the stock a body manifolds on. I spent a couple hours with a die grinder to open them up and remove restriction where they pinch way down.
Unless you are using the 340 manifolds that flow better it would seem well worth your time.