You'll need a Ram ball for the bars (or wherever you want to mount the base), a Ram extension (tubes of various lengths available; each end embraces a Ram ball); and, some way to attach a Ram ball to your GPS receiver, plus a way to plug in the GPs receiver for power (either USB (5 volts DC), or 12 VDC; the latter through the GPS receiver power plug; conditioning the electrical power; reducing 12 VDC to 5 volts).
A Ram cell phone carrier just might hold your GPS receiver.
That said: Your auto-style GPS receiver might not withstand the weather exposure and high-G shocks motorcycling provides; the Garmin motorcycle products are pretty robust in the motorcycle environment.
One note: A USB converter, 12 VDC to USB 5 volts, draws current when connected, whether GPS in use or not. Will wear down a battery in time. Some USB converter claim they turn themselves off automatically, perhaps when battery voltage descends to 12 volts, but . . . do you feel lucky, Pilgrim? I unplug when parked; YMMV.
If I get ambitious, I'll post a picture of my GPS Ram mount assembly on my KLR.
“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre