Hi Lewis,
There are many posts on the web that suggest using rings to reduce flexure of the tube to help maintain precise collimation. If you've got them and they fit, I'd be using them.
As for the collimation, I'd suggest trying to adjust the primary mirror first. In addition to following Vixen's instructions, I used a laser collimator to align the focuser and secondary, so they're probably pretty close.
All the best,
DT
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