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My Lumicon OAG is also plenty big enough to not impede the light onto the imaging sensor.. I did as Fred mentioned, I measured the OAG's mirror offset from the center of the barrell and created a FOV in Starry Nights to show me the ST8300's FOV, and the relative FOV of the guider... This has made manually setting up shots easy... I can frame them how I want within the imaging chip whilst having the guider at the right angle to detect a star...
As for other equipment.. You may need extension tubes or a parfocalizing ring ( I use a parfocalising ring ) in order to focus the guider.. You may also require different spacers depending on what flatteners you use etc.
I currently have the OAG before my flattener, which sucks as 1/2 of the guide chip gives me distorted stars that aren't too useful for guiding.. I'm looking at upgrading to the TS OAG9 from Teton Telescopes in America. It only takes up 9mm of backfocus, so I could easily fit it between my CFW and my flattener. This would provide me with a full field of sharp round guide stars....
The only other consideration you need to make is whether or not your focuser will handle the load... I've got a 2" FT on my TMB refractor and the focuser sags under the load of my setup.. I need something better.. but can't think of what will do it? My whole setup, (Camera-CFW-extender-flattener-OAG-Guide cam) weighs in at about 3.1kgs.. The focuser does not like the load at all... I dare say the focuser in your 10" RC wouldn't handle it well either...
Best option in that respect would be to add extension tubes to get you within 1.5" of the focus point, then add something like the FLI PDF focuser.. That way your whole setup is a single, thread on, solid piece.. with the PDF allowing for 0.5" of focus movement.. This way your setup would have 0 sag, and focusing would be automatic too....
OAG's definitely have their upsides, but there are negatives to consider.
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