Usually aftermarket exhausts "in the day" came with some way to solve this problem, just a steel bar that bolts into one of the original exhaust mounting bolts. This part naturally gets lost over the years but you should be able to make something pretty easil. Check on the opposite side from the chain, the stand probabl;y passes close to a bracket with a bolt hole. Just get some steel bar and bolt it on. Adding a rubber pad is nice too, cuts down the clunking over bumps.