hi. headman race step header fits stock suspension with a little tweeking . 69 dart 416 b1ba 904 has gone 9.80 136 3050 lbs. less driver full glass car only glass hood. have to carry weight to stay in 10s. trick to heads is move intake push rod. need offset rockers. then you can plug that big pushrod hole. and port finish . hugh difference. just thought i could shed some light.