I upgraded the Z-column on my Sherline 5000 vertical mill recently. The upgrade moves much more easily than the older design, but if you can't spring for the money for the new one, or you want to construct a specialized precision jig of some sort, this isn't a bad choice.
I also have a couple of the spare hand wheels (the smaller ones that you can't reset zero on).
If you are interested, let me know.
snipped-for-privacy@claytoncramer.com