I'm back!
(Probably part time again... been busy with some home renos - mostly done now, I need to update my pics)

BGasser, Yes I did solve the issue with the fit of rack and pinions. A spacing issue of that plastic nut (removed that nut and replaced with a washer)
Very close fitting, but there is clearance through the entire travel on the rail.

My next issue with the machine is the Y axis pinion mechanism. For a 'kit' project, it hasn't been a straight forward project... seems like every time
I get one step in, I'm stepping back to fix/modify parts to make this whole thing go together...
I now have to take the Z axis back plate out to mill some clearance into it.