I have two Losmandy Dovetail Plate Adapters for sale.
This is the description from the Losmandy website:
"Mounts to existing rings or telescope. For use with dovetail plate. Once mounted, no tools are needed to interchange equipment."
A picture of these dovetail plate adapters can be seen at:
These show some signs of wear as the black anodized surface is worn off in some places; functionally they are perfect.
The dovetail plate was custom made at a machine shop to work with these. It is 9" inches long and 3" wide and 3/8" thick. It could be drilled to fit the mount you are using.
The plate cost $40; the adapters cost $75.00 = $115
Will sell for $75 plus shipping
Thanks for looking