I wanted to be able to level this bench without shims. And I didn’t want to be able to see the levering gizmos. Conflicting goals for which I came up with a very imperfect solution.
I found these heavy duty jacks at the scrap yard and welded up a tee nut hold them. Then carved up the bottom of the bench feet to accept the assembly (I used two jacks, mounted on the short side of the bench). Nice and invisible but a royal pain in the butt to adjust. I was hoping I would be able to slide a [very thin 19mm bicycle cone] wrench in there to turn the adjusting nut but that seems just about impossible in practice. Tilting the bench up and putting a 2×4 under a foot makes it reasonable however. And they do work very well at leveling the bench – I was surprised how much my “über” stiff draw-bored-mortise-and-tenon base will twist on an uneven surface.