B-303 cam with stock oem h-pipe

i may be mistaken, but most iemts like that read for off road use only are labeled as such because most people tend to run them on cars without smog control systems. the x pipe on my 90 5.0 was listed as for off road use only, but they only make them for 5.0's. so i imagine you would be safe with that combo. as far as the clogging question, i'm sure any mullfer shop could tell you. and i would get more than one opinion, since they might try to hit you with the ol' sales pitch.