For what it's worth, going to a solid column or adding a bracer to the existing column will make a HUGE difference in rigidity. After that, get good quality bearings and grease them correctly and you should be set. In my case I went to tapered roller bearings with proper spindle grease, (Kluber Isoflex) at the right quantity per bearing, and added a shaft oil seal to the lower bearing cover to keep crud and swarf from entering the bearings. (The seal was specced for the diameter of the spindle, spring removed, and frozen/cut down enough to remove almost all friction as the spindle would heat to an alarming level without the modification. For those curious, I used a carbide boring bar with a high-positive-rake ground/polished cutting bit designed for aluminum, and it shaved the rubber like it was something far less flexible). I also originally bolted the machine down to a plate that extended half-again as long as the base behind the mill. To this, I bolted a diagonal bracer to the back edge of the plate, and just under the electronics box on the back of the column to improve rigidity. I recently bought the solid column kit and it looks pretty nice quality. Column is probably twice as heavy though, compared to the original, so be aware. I intend to tram the column to the base via shims before I transfer all the parts between the two, as the whole thing will become more challenging to manipulate once fully assembled.
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