I also use the iron aces mount. but I added another swivel to it that allows me to tilt my 660 up/back/left/right as needed.
if you use the garmin wiring harness, you can run the aux plug to the audio input on your hk (this is obviously for 2013 and older), while running everything through the instrument nacelle and then down under the tank. removing the tank is easy, and there is a plastic channel under it. remove the lid, run your wiring, replace the lid. wiring is nice and protected. get the aux plug from iron aces, and you can plug into the aux plug under the seat and your mount will be powered by the aux switch on your dash.
it only takes a little longer to do it right, and then it's done and you won't have to do it again.
this first pic shows the swivel. $15 from amazon.
this pic shows the routing of the wiring. yes, the zip tie is blue. its what I had
.... it would be very similar for a rushmore model, except you would have to purchase the additional aux input harness for the back of the infotainment and would actually be a cleaner install cause you wouldn't see this wire all the time. eventually, I will be sending my radio to iron cross audio and getting the rear aux input install done.