Gantry type milling attachment.

[Toolmaker51]

Thanks Toolmaker51
You have given me food for thought on adding threads to the pillars.
I must admit I would struggle to make the raising blocks now as I no longer have access to a surface grinder (just a couple of lunch hours at the time).

Is surface grinding to square the riser block pads to centerline of post and/or threaded portions? Dissecting the photo hinted slight design alterations to work around that. I'd turn, bore, face to .0002 perpendicular, and recess additional blocks in diameter equivalent to square size you already have. Drill + tap matching 4-hole patterns in new pads and existing pads, also tap new pads adjacent to clearance holes for jack screws. Could assemble and set up with surface plate and cylinder square every bit as accurately that grinding might produce.
Or I completely misinterpreted details in said photo...At any rate, despite having enough mills and a great lathe, I'm considering your modification. Vertical for sure, maybe horizontal spindle for weird work like Higbee thread starts. Still use rotary table and mill now, additional setups. But then most have only CNC programming solutions, or have to ask what are the cuts for?
Phffft.