Retrofiting an old big milling machine

I have contacted diamand polymer and there is a communication problem.
I asked them about their products they answered me after 2 weeks with a generic mail
and after that i asked them many times for EU moglice supplier without any response.
Seems more easy to buy moglice in US than EU.

Ballscrews for X/Y 32 or 25mm are cheap but 65mm for Z is expensive.
The brushed DC motor that have now is 100V 26A 1000rpm moves up/down Z axis
without problem but i have big servomotors > 3kw so motor is not problem for Z.
The question for Z axis is the backlash if keep existing leadscrew the weight
of table theoretically eliminate backlash automatically..
Exists any use case that backlash can appear on Z axis with leadscrew ?
If i can hold Z axis leadscrew then X/Y is ok to replace leadscrews with ballscrews.

Before make full retrofit i want to retrofit it as is mechanically...
Because must use that machine for some machining of some parts
(adapters servomotors motor plates etc)..
In that machine each axis moves separately from the same dc motor via electromagnet gear engaging(3 electromagnets)
The dc motor driver that moves all axes (X-Y-Z)  accepts pwm and each axis has linear scale that outputs AB incremental quadrature signals(i have replaced linear scales with new ones).
I have a mesa 7i80hd with 4 axis analog servo daughter card.
Some examples how to do the linuxcnc configs ?
I don't want 2 axes the same time moving no 2-3 axis interpolation
just moving 1 axis each time.
How i will make the selection which electromagnet will be engaged ?
For example if i have code G0 X100 how the electromagnet for X axis will enabled
of if i have code G0 Y200 how the electromagnet for Y axis will enabled and disabled the other 2 ?