Thinking out loud...

With the drive to the quill rack, probably from the left side as done in the FlashCut kits etc, without measuring i think the quill pinion does 2 full turns for full travel so about 75mm/turn, with a 4:1 or maybe 5:1 belt reduction from servo to pinion shaft, would that give enough resolution/torque - the motor would only ever do 8 or 10 full revs??

I could probably make a bracket pair which could take one or two layshafts which could offer much higher reduction ratios.

Maybe even look into worm-gear reduction.

Just working things through...