An update.
I got the adapter above and eliminated the focuser from the collimation process since I was able to directly attach the tak scope to the RC10. The semi-good news though is that the focuser appears to be well collimated anyway as there was no visible change to what I could see.
I tried to do a collimation without touching the primary mirror, however I couldn't get the dot in the secondary to line up properly (within the little circle of the tak scope). I made some adjustments to get the larger circles aligned nicely (expecting though it wasn't going to work).
I then looked at the results under the stars. Out of focus the stars looked mostly ok, but when I moved close to focus it was quite obviously wrong - they looked like they had 'v' shaped wings (like a winged viking helmet).
It's at this point I made things worse.
I tried to adjust the spider vanes on the secondary to see if I could get the secondary lined up - no go, they're basically locked in place. I then unscrewed the secondary from the spider to examine the system further. While it gave me a greater understanding of how the push/pull system worked, I couldn't see any obvious mechanism there that would help with aligning the secondary dot to the primary.
I put the secondary back on and adjusted the collimation as best as I could. However, when I went to do a star test - couldn't find stars or get focus. At this point I realised I had severely messed up the distance between the secondary and primary mirror and had probably reduced the focus to somewhere I could now not reach.
Ok, time to find out what distance to set the secondary (the push/pull screws) and/or find out the distance between secondary and primary. Googling away hasn't given me any details though. I have found figures I think for RC12 and RC8, but not RC10.
Anyone know the figures required? If anyone has a GSO RC10 (closed tube if it matters - I've got a CF) that have a collimated scope and could measure these values, that would be great.
Back on the secondary dot and adjusting it to align - I'm open to suggestions on this as well. I'm going to see if I can get a laser to check that the dot is really the centre if I can determine a way to attach it without potential tilt.