My '66 GTO has a solid roller with Doug's round port headers with 3" exhaust all the way back. I used Dynomax Super Turbo mufflers which were fine drone-wise, but too loud. I added resonators downstream of the mufflers like the stock setup was, which made a significant difference. The body length of the 24222 is only 12" long and looking thru it you'd swear it wouldn't make a difference...but it does.
https://www.dynomax.com/mufflers/rac...ullet-mufflers