Hi Pat
If you're referring to this page:
http://www.admaccessories.com/D_Series_Dual_Saddles.htm then you'll probably need only the DUAL LOS8 - this will allow you to use any dovetails that are either Losmandy or Vixens - so you'll be able to get away using the Vixen dovetail bar that is under your OTA unless you have the wider type which means that it'll fit the wider part of the jaws (Losmandy style)
Think the DUAL M8 you mentioned is actually for the Tak using M8 socket head cap screws
HTH
Cheers
Bill