I found this site today and thought it was another good mechanical alternative for cruise control. I couldn't find the R3 listed so I contacted them and got this response:

The BrakeAway P/N 5CPO2 will fit your Rocket lll. It is not on our fit list because the cruise control will take up about 3/4" of your grip space. For someone with large hands this will not leave enough room. Some people trim down the flange to give them a little more room.

Regards,
Kim Fechner
BrakeAway Products, Inc.
(503) 892-4998
www.brakeawayproducts.com

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I used to compete in sports a lot, but then I realized that you can buy trophies......So now I'm good at everything.

I have one with the Kuryakyn grips which are longer than stock and it works great. I am very happy with it, a real quality piece.