under or over diff exhaust.

[NoHachi]

Jon, dunno, but you could try and use the following trick that we used to use for our dyno-exhaust setups..Instead of dropping the money on expensive mandrel bent pipes, we would just grab a piece of pipe, weld one end closed and stuff it with sand. The whole thing would go into the bending machine and we would heat up the outer curve section of pipe with a simple gas-torch.
While not exactly mandrel bent, the end result was good enough. Maybe 1% less performance then true mandrel bent.