I would have some concern over this adpator on top of those rings with just 1 1/4 inch bolt holding it all. despite the light guidescope that is going to flex.
You may get away with it at short focal lengths but go longer and you almost certainly will have issues.
I would attach a losmandy saddle plate on top of the scope between the guiderings and then use 2 guide scope rings to support the 50mm guide scope. this will allow you to slide the whole guide assembly back and forward as well to help balance the rig.
Her is a link to the rings you could use:
http://www.bintel.com.au/Accessories...oductview.aspx
And the universal plate:
http://www.bintel.com.au/Accessories...oductview.aspx
You can also get a short universal plate. This system is rock solid and exactly what I use.