whow, never seen one like that before. it should have a flange with a hole in it. on the flange there should be a 6 bolt pattern for the Supertrapp disc's to mount to. this looks like someone cut it out alltogether and welded in a plate.
Are you the first owner?
other than looking on Ebay for a supertrapp or other used Lc4/SXC pipe I don't know what to tell you.
sorry, good luck.