i have an 05 wrx...and i have a borla xr-1 2.5 ich cat-back that i would like to put on. i was wondering if anyone has the same set up.i have a perrin downpipe and soon to be xr-1.will the cat-back bolt rite up to the perrin downpipe or am i gonna have to get a 3inch flat flange to get it to fit?b/c the exhaust came with a donut style flange.