yes trim off the pinchweld & reweld the seam (it needs the strength) then mockup. You may or may not need addit'l floorpan work. I would highly suggest a 904 instead. You do NOT need a 727. #1 will be exhaust selection (manis/headers) for adequate flow.
View attachment 1715266256I was able to find a 904 and got some parts to rebuild it as well so going with that. Your Dart looks great...