Filled with some sort of cement specified for this purpose (filling of hollow structural beams and machine bases) + a few pounds of lead for good measure.Filled the column with what?
Post some pictures of the extra hardware to maintain registration please.
I added linear bearings and hardened shafts to maintain registration when lifting the head. The linear bearings were an Amazon thing that came as a pair so I decided to use both.
I did one other thing that also helped, I added thrust bearings to the three column clamping bolts, and then made permanent long handles instead of messing with a wrench. This was really worthwhile because I tighten more with a fraction of the effort.
I also added a surplus Princess auto windshield wiper motor to replace the crank when lifting the head.
All in all it makes lifting/dropping the head a near painless experience compared to the original method.