Dave, I use solid tube rings around my main OTA with a Losmandy bar on top which I can clamp another set of smaller solid rings on top to hold my Orion short tube 80 guide scope.
Don't bother with adjustable guide rings, get the solid ones instead to minimise flexure.
These rings just clamp around the OTAs and you tighten the knobs to hold them in place, no need to drill any holes in the OTAs.
I've also got another Losmandy bar on top of my short tube 80 so I can piggyback a camera as well if I want widefields.
I don't have any pics atm and I'll be logging off soon but I'll see if I can find some pics and info for you.
