I've got hold of a ZXR exhaust and want to keep the shell only (this is for a project of mine)

The end cap has three welds onto the main exhaust as shown below



I've used the dremel to get rid of the welds but still can't remove the end cap. I don't want to destroy the end cap as I want to reuse it. The end cap does have four round holes around the protruding baffle which I can use to get some leverage to twist the end cap. Unfortunately all I'm doing is warping the four holes.

Anyone have any ideas on how to remove the end cap?