Just been given one of these, a bit tatty. Had exactly the same thoughts about pcb milling and for that pcbgcode and linuxcnc would be an an obvious choice but I am also up for selling as is if someone need a donor machine, It moves and homes but the spindle does not come on from the panel buttons and the spindle drive belt is broken. I think GRBL would probably work well but it also seems like a very fiddly job to overlay a retrofit onto Rolands design