[RC-Monster Mike]

There aren't a whole lot of G1s out there - no idea exactly how many, but when I won the G1, GorillaMaxx was brand new and the G2 came pretty quickly. The G2s should be the most available(though the G3 is largely the same, but with thicker plates and no "short" version).
The Gorilla motor mount is compatible with the single speed - the Gorilla mount is not very rigid, though. The 2nd generation gorilla mount was better, but still not stiff enough for common motors around today.