I see in Mathew's
www.telescopes-astronomy.com.au newsletter he has cheaper options than ADM. To quote:
CONVERT YOUR MOUNT TO LOSMANDY TYPE "D" DOVETAILS
Convert your SkyWatcher, Celestron, Vixen etc. Mount to Losmandy style "D" Dovetail Plates. This conversion improves the rigidity of the Dovetails used from the narrow "V" Tails to the extra sturdy "D" Tails. Particularly good for Astrophotography. The conversion uses a new Replacement Head for the Mount, and the new Female "D" Dovetail. The Female Dovetail can accomodate Losmandy, CGE and William Optics Dovetail Plates.
Replacement Heads $55
Female "D" Dovetail $95