i got a 100cell 5" body cat, with 3" inlet and outlet, was told it was a direct bolt on, for r33 and 180 apparently take the same cat...
i connected mine up with a jjr tront/dump but didnt fit, the dump pipe needed to be heated and twisted, and flanges aligned to fit,
thought it was just my car as the exhaust shop said it was the front dump rather than cat,
but my bro with his 180 had the same prob, so i think they had an issue with their cats, i did contact george about it and he was really good,, he said he'd look into their design,
even though it wasnt a direct bolt on im still really happy with it.