The Wimberley P-20 does not have a 1/4"-20 threaded hole on the bottom, the RRS L84 does. The L84 is also about 1/4" shorter than the P-20, if that matters.
Rather than screwing the BR lug into body or lens plate, I'd suggest attaching the lug semipermanently (Loctite Blue 242) to a small AS clamp. RRS has the B2-FAB-F, which is a 1.5" clamp. I prefer the smaller Kirk QRC-1, a 1" clamp - I have one on each of my two BR straps, and I can easily and securely move the attachment point from body to lens to another lens or remove it for tripod/monopod mounting.