[Freon]

I wouldn't bother with the factory intercooler if that's what you meant. The clip connectors would be more trouble that they're worth.

No idea on mounting and such, though. My guess is you'll be hacking away a bit on the bumper and making a few brackets that don't exist on the 128i to hold it in place. The bigger problem might be interference with the radiator or AC condenser, again, no idea, hopefully you don't have to swap out the entire radiator and half the AC parts from a 135i to make room regardless of what intercooler you get. Also keep in mind properly shrouding the intercooler and sealing it to the bumper is very important for proper airflow through it. Air would rather go around the intercooler and radiator (i.e. under your car) than through them if the path is easier.