I've had work done at A&A Motor Werks (
http://www.aandamotorwerkes.repair.bz/) and was very pleased with them. TBH that type of swap wouldn't require a BMW specific repair shop tho and you might get a cheaper labor rate elsewhere. All of my other work I trust to Sean @ Munky Wurks Garage next door to the Best Buy in Iwilei.
I wouldn't worry about any problems or downsides to doing that upgrade.