Pic from ADM. The plate I have is the 2nd from the right with the 5 lengthwise holes. The spacing centre to centre of the holes is 5cm (2") and the width apart is also 2" centre to centre (or 2.54 cm to the centre hole where applicable). The only difference is mine does NOT have the 2 closely spaced holes at each end (only the centreline small safety screw hole).
http://www.admaccessories.com/D_Series_Universal.htm?
ADM's blurb: "DUP11- 11" Universal Dovetail Plate for Losmandy style saddle plates. .5" thick. Will fit G-11, Celestron CI700 mounts. 11" long with one 4.5" long slot along the center for 1/4"x20 socket head cap screw or 1/4"x20 button head cap screw. Holes are 2" apart center to center to accommodate Parallax and other style rings. "
Price new is $65 US without post... how does $50 Aus posted sound?