Playing devils advocate there and like some opinions for and against with the two methods described below.

Both methods will rely on a tranverse mounted stepper motor at the rear, this will drive two pulleys, one either side via jack shafts.
All pulleys will be well supported on bearings.

Two lengths of open belting will pass from these pulleys to twin pulleys on the front of the machine and the open ends will be secured to each side of the two uprights.

Basically open belt drive to replace two ballscrews and this will be over a 1 metre length at max, probably more like 800mm.

Now the different design points.

Plan A will have one end of the belt secured on a fixed bracket and the other on a bracket that can be adjusted on a turn buckle.

Plan B will have both ends fastened to the same fixed bracket and adjustment will be handled by independently spring loading the front idler sprockets.

Thoughts on this please ?