Not everyone's cup of tea. 71 Demon
I kept the sub-frame connectors (one of the few things that I kept) that where on the car when I bought it. The connectors cap over the rear frame rails. We used a 4" hole saw to drill through the connector and the frame rail then we cut an old 4" concrete boring bit to use as the inserts. Now I have room for 3" pipe to exit.
I don't know if this was a smart thing to do or not but it seems pretty strong to me.
These pics were takin before the welds were dressed and re-painted.