66' Barracuda and 273 with headers

here's a question for you all ........Could I see any improvements in performance / horsepower on my built 273 with 1 5/8" hooker super comp chassis headers with 2.5" collectors vs hedman full fender well 1 3/4" 3" collector ? or would 1 3/4" tubes be too big ?
possibly might use the hedman 1 3/4" fender wells on my new 273 rebuild with 10.5 compression and big erson cam 286 dur 510 lift ...similar to the d dart engine.