My very first post to this forum guys. I was kind of hoping to find a design for some sort of double wedge adjustable height device for four-way post, but it looks like it is shims or shims. I am long retired now, and use the machinery at the local Menz Shed. This is the metal lathe we have
https://www.machineryhouse.co.nz/L141
It came with a set of tools which all have the same height, so it shouldn't be a big deal. We also have a small mill drill, so I could machine a one piece shim. The only problem being to measure its thickness when four or five assorted thinner shims are uncompressed. Put them in a vice and measure as close to the jaws as possible would do it. Another problem is that I did do this once before, but one of the shed members helpfully tidied the one piece shim into the scrap bin. Perhaps the next one will go into my tool box.