So I realized I have been overthinking the drill press.  I really just needed to use some 2x4's to hold the wheels on.  This works so much better than the 3/4" plywood, there is no flex in the board that I can detect.

I had to cut out a small chunk out of the back board to fit it in around the base of the pillar. I offset the bolts a bit to minimize the amount of material I had to remove.  It seemed to have worked, it is still very strong.

This works well, but there is still some flex in the casters, even when locked.  I don't know if high end casters are more stable, I suspect not.

I went ahead and cut a notch in a 3/4" piece of plywood that was 24" square.  I'm going to attach this to the base.  There is just enough gap between the top of the wheel lock and the base of the plywood to get a toe in to lock and unlock the wheels.  In theory I could cut this down from 24" to 19" wide, if I need the space.  There is a bit of room on the back to reduce the size as well, however the motor on the back of the drill sticks out a good bit past this existing base, so there is probably not much point there.

I found the time to attach legs to my old fold out work top.  It is quite ridged!  I have not added in any side braces or a shelf yet, I have not decided how to use the space under the table.

I temporarily added a small wedge of wood to help secure the wheels to.  This could be replaced by a side brace or other item at a future time if needed.

I set this up to be 38" tall when all put together.  However that feels an inch or so too high to me.  I may cut it down a bit, or may switch out to smaller 2" casters.  The 2" casters seem to work as well or better than the 3" casters in practice and would lower the workbench the right amount.

I picked up a sample pack of expansion crack fillers.  They seem well made, however they are clearly not a good fit for my expansion (compression?) cracks. 

Even if I manually cut them down the smallest ones would not get the job done.  I need to think of another solution for this.

Up next is reworking my main bench and possibly reinforcing everything.  I think I will go ahead and order a few more packs of the 2" wheels as well and see how I like them.  And I want to make a proper table for the drill press that matches the base as well.