yea, when i put my mac o/r h on, under certain circumstances it feels like it is hitting the floorpan. my cousin has a similar problem with his bbk o/r h on his 91 stang.
i have had the problem for three years and no matter what i do i cant fix it completely... the problem is that with the angle of the h pipe, i can only adjust things so much, and the pipes that go over the axle have about 1/4" clearance to the upper control arms and about 1/4" clearance to the frame... my only fix would be a set of aftermarket control arms that didnt have the sheet metal bend like teh stockers do, ugh, good luck you might be in my situation