Another update...
Decided to take everything apart again and use the original decorative backplate and the focuser baseplate, after reading a few posts on CN (fyi, I used longer 3mm bolts).
End result is that I didn't need any washers, but the focusing rod still wobbles. It appears that this is indeed related to the grub set screw which tightens the plastic insert onto the brass rod.
Looks like I'll need to solve this before proceeding. I'll probably get a piece of thin plastic to wedge into the opposite side of the set screw. Others have used electrical tape around the brass, but I don't like using electrical tape as the adhesive tends to degrade over time, resulting in a mess when removed.
https://www.cloudynights.com/topic/6...o-8/?p=9543853
https://www.cloudynights.com/uploads...3249_thumb.jpg