Got all pieces for my RSR GT2 exhaust-so anxious to get it in. Problem: an extension is needed between mid-pipe and y-pipe, i don't know what size that extension has to be. I was given an estimate by RSR which is 10" but I'm not welding the extension on. Instead, I'm putting flanges on it so i need to know exact measurement. Cant find people with this exhaust so please help.