Not had much time but a bit of progress on this.

Replaced the original x axis stepper with a Nema23 which was a direct swap, bolt holes all the same etc.

I ordered a cheap chinese motor controller which arrived today and seems to work well - motor is dead quiet and smooth. It's running off a potentiometer so need to figure out how to get that controlled by software at some point.

https://www.ebay.co.uk/itm/282820954577

I have a fairly simple plan for attaching a Nema 23 to the Z axis so hopefully get that done next week.