When I had the hedmans and the 3" headpipe, I didn't have a problem.
After I put on the World Products, I found out they gave a "raised exhaust port"?. The head pipes then contacted the crossmember. When the motor would lobe/shake, the pipes would clank! awful.
I used a heat gun (the cetaline torch kind) and heated up the pipe, then took a pair of LARGE pliers and crimped it some. Not the most flow efficient, but I was in college at the time and had a friend at a muffler shop let me come in late one evening.
It still contacts some, so I stuffed a torn piece of exhaust manifold gasket in between them and tied it on with bailing wire.

My car rocks.