John, If it's very tight by the crossmember, I'd assume the 1/2" steel round stock that attatches to the transmission bracket already came welded on to your 4"tubing. Maybe not exactly in the right spot. This is always the last piece I weld on to the system. If that's the case, cut it off, move the 4" tubing to where it clears the crossmember, and then re weld the 1/2" round stock on to the tubing. You could probably fit a 6" exhaust through there in a pinch. (it would be very tight though)
Garry