It looks a lot like the same size as the WO plates.
http://www.williamoptics.com/wo_shop...products_id=85
I did the Losmandy D dovetail dance when I bought my WO rings as well, only to find that they didn't fit. The WO rings that I have look identical to yours.
I'm currently using a Losmandy DUPS shorty dovetail with only the middle screw in place for each ring, and I had to go out and purchase some machine screws short enough to thread properly.
It isn't as rigid as it could be with the WO plate; I really should break down and buy one.
Regards,
Eric