I have a Justin Browne SOS plate for sale. I got this recently but made a bit of a schoolboy error in that it's too wide for my Clipper dovetail...whoops!
This plate allows you to detach the complete camera assembly from the rig and clamp it straight onto a tripod head without the need to swap out the steadicam dovetail, a pretty neat timesaver!
Apparently, the plate fits PRO, XCS and *WIDE* Tiffen dovetails. It's in great condition with a few minor scuffs.
Asking for £140, based in the UK.