I know this thread is dangerously old, but I have the OBX ram horn, so I thought I'd chime in. The fitment from OBX directly conflicts with the thermostat housing. Its like they didnt even install it before they started selling these. Anyway, I cut the flange from my 4-2-1 NA header and made that into a spacer. Fixed that issue. But the #1 runner is still way too close to the radiator hose to inspire confidence. Ill see how that goes. With a T3/T4, compressor side to the passenger side, and an external WG to the drivers side, AC needs to be removed, as well as the tensioner pulley (duh). Space between the turbo and starter is not too bad. Only one full size fan will fit though (drivers side).

Ill update if anyone gives a damn once the car has seen the street.