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Thanks for the comments Marc. I apologise for my lack of clarity, I have been trying to keep the posts short and not hijack the OP's threads. Perhaps better if I start a new thread on my concept and put all the gory details there. Just handy to have all your comments in one place!
However...Just to clarify my previous mirror-tube comment, presently there are two concentric "tubes", the inner baffle tube that's attached to the rear casting (how?) and the outer "Mirror assembly" tube, apparently consisting of mirror, various bits of wood, rubber and metal focuser bracket, which slides up and down the baffle tube, moved by the one-point offset focuser threaded rod.
My concept is to add a third concentric ~40+mm OD aluminium "focuser tube" inside the "baffle tube", and of only slightly smaller diameter, and extending out the existing rear visual back, where it can be attached to the inside of a Crayford draw tube to move it forward and back. It's then necessary to attach the other end of this "focus tube" to the rear of the "mirror-assembly tube (MAT)" via new baffle tube slotted holes for 3x attachments to the existing metal focuser bracket, to move it back and forth for focussing, while still having the MAT basically supported as usual by the baffle tube. The old threaded focuser rod would of course be removed.
The new inner "focuser tube" would not support the MAT, just move it back and forth via the Crayford drawtube movement. The "baffle tube" slotted holes I was referring to earlier are to allow a connection from the inner focuser tube to the outer "mirror assembly tube" as it moves to and fro over a very limited (40mm?) range for focus. As they don't carry any of the mirror weight, these "connections" shouldn't need to be too hefty.
Clear as mud? I think a new thread is needed. Of course, if one was brave and ambitious, one could also incorporate your collimation feature........Sow's ear and silk purse for a C8 comes to mind though.
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