Sorry 'ol mate.. but isn't the MAP640 a marine gps unit

but if you want to put it on a 12GS then its Ok with me
so long as it floats your boat
Onto the back of the Garmin cradle with a RAM-B-347 plus screws as shown, then add arm, RAM-B-201 standard or short RAM-B-201-A with RAM-B-231Z u-bolt (use 1" and black shim) add a rubber strip as well to protect and go onto lhs of clocks on screen support.