Excellent pics Clive, thanks (do you have a build log?)

I'm assuming the slot in the bed and moving the replacement ballscrew up is needed to clear the Y axis carriage below it? I was rather hoping to get away without modding the main milling structures (beds etc.)

BTW - when you milled that slot were you using a 2.2Kw Spindle on your router? I've not tried running mine that slow as I thought you got torque issues below 6000rpm?

The Z axis looks like it could be converted by using a new top plate/bearing holder with a stepper/belt arrangement essentially strapped to the back of the column and abandon the "differential/bevelled gears" from the original?

Looking forward to seeing more progress shots.