If you’re not bothered about using the thumb wheel for navigation, it should just be as easy as changing the mount. Personally, I really liked the integration of the wheel with the nav, so wouldn’t want to lose that.
Think about using a 276CX ! It's a good, solid navigation unit and IMHO, a way better choice by a loooooong stretch
or a Montana 680
or a Monterra (if you want music too)
or a 66i
or a 64ST
all of the above connected to my 'pogo' stick.
On some of the more modern Garmin devices, the power cable is the same, so the OP may be able to use the same cable.
The power cable for the 396 is the same as the XT, but the bracket is different. If the OP can take the BMW mount apart, he'll see if the cable is the same.