I bought a RRS B2LRII in 2007 to mount on a Manfrotto 488RC2, replacing the Manfrotto clamp.
I currently own:
RRS L-bracket for D70s RRS L-bracket for D300 (no grip) RRS L-bracket for D300 (w/grip) Universal plate from eBay sellar Hejnar Photo (krosnos65)
Hejnar claims compatibility w/RRS and I've found that to be true - no issues with the RRS LR. In fact, I bought one his L-brackets for my son's D50 and that also fits perfectly - both clamp and camera.
I was glad to read the comments on the Markins clamp as there's a nice savings vs. the RRS and adds to the options for people considering the move to an AS system.