usdm itr header on a DB2?

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I have a guy who is trying to sell me a usdm itr 4-2-1 header. Now I know that all b-series header will line up but, will it fit with no mod?. So will the itr 4-2-1 header line up with my stock cat? I did a search and i get different answers on the collector size for the usdm itr header. one forum said its 2inch and in another its said it's 2 1/4inch. Now i know its not 2.5inch or am i'm wrong? So will a usdm itr 4-2-1 header fit my 92 integra gsr? if not what mod will i need to do to make it fit?
the type r header has a 2.5" collector, as does the b18 gsr's. i don't know if the b17 gsr engine had one as well though. if they don't match i'm not sure what the best way to go about mating the two would be. cause somehow you'd need to get a 2.25" flange welded to either the itr header, or a 2.5" to 2.25" adapter welded to your stock exhaust.