Well, I just thought about it and I measured the studs that come out of the resonator and it measured around 4.1" center to center so that makes sense that it would be a 2.5" flange. Walker PN# 31896 says its a 4" bolt pattern, which shouldn't be an issue. If that's the case then the gasket would be PN# 31337.

I should be able to get everything I need except for the band clamp at Advance for about $40. I might just pay my buddy a few bucks to weld the flange on for me.