Have a 351C, 4V & 4Vheads that I'm going to be replacing headers on because of a ground clearance problem. Exhaust kits for this 70 Vert seem to be mostly 2 1/4". Is that OK for this engine, or do I need 2 1/2. What was stock size? Looks like 3" are on there now and that's way more than I need. Car will be a street car, not drag car. Also, flowmaster 40's or 50's?--looking for nice deep rumble, but not real loud. All opinions, recommendations welcome.