Guidescope for 12in LX200

[jabberwock48]

Would anybody have any suggestions on a suitable guidescope/imager to be piggy-backed on a Meade LX200 Classic 12in. I was thinking of using the Astro Engineering mounting rings that attach to the front and rear castings unless anybody would advise against them for lack of rigidity. So this means the tube length would need to be a minimum of 50cm. I guess another consideration is that too short a focal length would not be a very good match for good tracking. Ideally I would like a scope capable of good imaging of at least 80mm objective to have the flexibility of guiding via the SCT and imaging via the refractor. I am planning to use a Canon 450D as a camera but am undecided about a guide camera. Thanks for any advice