[Freon]

It would be pretty epic to have an AWD 135i, but what everyone else said.

My guess would be transplanting an entire 335xi AWD drivetrain is your best bet. Entire engine (longblock), transmission and PTU, front diff, front axles, front driveshaft, suspension knuckles, possibly other bits of the suspension (??), possibly the even front subframe, ECU, and wiring harness. More like a 135i shell on top of a 335xi. You'd need a custom rear driveshaft, probably the correct rear diff to match the front diff drive ratio (probably the 335xi rear diff itself, hopefully fits).

I'm not sure you'd want to actually rewire. Taking the whole harness and ECU from the AWD car might be more practical. Wire loom locations and routing might be an issue.

Who knows what sort of issues there may be with the steering rack, too...

Anyway, it would be cool. Could be the ultimate STI/EVO killer for quadruple the price...