I received these rings and mounting plate with the purchase of an older AP 155EDF last year. These rings and plate are heavy duty, yet very well made. The Base Plate is 3/8" aluminum, 23.8 x 9 inches, and the rings are black felt lined, 1.5" wide. The rings do not hinge, but are cinched down on each side with a 5/16-24 stainless cap screw. I guess the original owner wanted to be sure that the EDF wasn't going to flex or fall. If you can use the rings (they're mounted to the plate with 1/4-20 flathead allen screws)they will fit a Losmandy 23-3/4" dovetail plate. There is nothing dainty about this hardware, but then, it is built to last. I am including the allen wrench, which is too big for anything else I use <g>!
Yours for $50 plus shipping.
Thanks for looking!