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?