I have a Meade 2040 4" SCT with all the Losmandy mounting accessories to attach to a Celestron 11" SCT. This scope is a small portable scope on its own, with a Thousand Oaks solar filter (I use it for more solar observing than just about anything else), tabletop tripod, DC drive, red-dot finder, improved celestron 25mm finder, and custom plastic carrying case. Just unscrew from the base and you have a 4" 1000mm guidescope.
One caveat: the scope has slightly pinched optics, which only affect high-power visual observations of planets and double stars. It still works great, but I'd rather not sell it on its own with all the ETXs to compete with. If you use it as a companion scope for wide field viewing, solar observations, and guidescope, there is absolutely nothing wrong with it.
The two losmandy 5" adjustable rings attach to standard dovetail plate (I will include the plate for the C-11, or you can get one to fit your scope). This with an added bonus. When you attach the guidescope stuff, it normally displaces the piggyback mount location (it's either/or with the Losmandy equipment). I remachined my old Losmandy sliding piggyback mount to attach to the top on both sides of the guidescope rings, for two configurations or theoretically two simultaneous piggyback shots. Bogen head included. I might even be able to include a cheap pentaxK style camera to use as your piggyback friend while taking prime focus shots--Kill two birds with one stone!
All this would cost over $1000 new.
I'm offering it for $500 + S&H.
Also have the 11" for sale, and the guidescope above for $400 if you buy together. See CG-11 ad.