I know RRM sells a High-flow cat that has the flanges already on it to bolt right up but I already have a cat sitting around. Is there any company that may have the correct flanges that I could weld up to the flangless HFC I already bought for my car?

 

the muffler shop should have some already. if not, check with www.roadraceengineering.com and look for the DIY parts. you might have to click around.

 

^^^ Yeah, a "good" muffler shop already has flanges sitting around for that use...

 

When I made my test pipe I just cut the flanges off of my old cat (was garbage anyways) and welded them on.