Hi Doc,
Long ago, I converted my Manfrotto 468 MG from RC2 to Arca Swiss by using a replacement clamp made by Wimberley. They soon after discontinued this and replaced it with a clamp that fit more models, but a quick look at their site didn't reveal this one either at this time. Hejnar Photo does make a number of AS clamp conversions for specific Manfrotto heads though, and he's very committed to customer service, so a call or email might get you some good information. I replaced the RC2 QR on my Manfrotto tilt only monopod head with a very inexpensive Vanguard clamp from Adorama a few years back also. OEC Camera is a possible source for inexpensive generic clamps, if you don't mind possibly doing some mods to keep the clamp solidly on the ball stem.
Hejnar Photo Store, Serving Your Professional Photography Needs Oec Camera
Scott