Attaching the column to the cheeseplate with just one screw introduces some elasticity and there is not much you can do about it, unless you attach a bigger plate or add a counterweight for balance.
If you attach the baseplate rotated by 90 degrees instead of having it point in the direction of the optical axis, you could add shims to compensate the tilt. Shimmed my setup for a while until I came across this device that is mostly used in astrophotography.
Also tried the 7 Artisans 60mm macro lens and found it did a good job, specially considering its discounted price of 130.- Tried with a few old slides that were sitting it out in a container:
Top left: Camera adjusted with mirror, the viewfinder grid does not show though 
Low left: Kodachrome slide taken and developed in 1972. Colours were good, no correction applied
The dark violet slides are Agfachrome, developed in 1985. No corrections applied.
The green slides are internegatives (virtual copies with inverted tone curve) that I had NLP convert to regain some of the colours. One could also improve the original slides manually, but going through internegatives and NLP is much easier. Note that success depends on how bad the slides really are. Some conversions will need some effort too.