Those manifolds are a 2&1/4" outlet so yes you'd see an improvement (tho I ain't sure how much) but as you know the ex is the most restricted part of the overall air pump (the eng). Muffler selection is important & I'd suggest some free flowing (noisy) ones with some glaspacks as resonators to quiet it back to a reasonable level. I would likely go to 2&1/2 if I was going to get a new ex system.I would do extensive dist timing mods & if it is an original Carter AVS then it is extremely lean & I'd convert to Eddy 2 step primary rods/short pri jets to richen it up. EDIT missed that it was a 72 so it would not be an OE Carter AVS. I saw the "70" for the manifolds