We have done one EKP retrofit for an RV-12 customer. The most difficult thing you'll run into is the physical placement of it. The wiring is pretty easy (send us the harness for the AvMap and we'll just build you a new GPS harness that'll plug into your current switch panel/board like your other GPS), so no hard changes there. We've had a number of -12 builders putting in other GPSes and radios, etc... and we're more than happy to help you to the extent we can.
Cheers,
Stein
PS - Mod's...feel free to move this to the RV-12 forum.