I have been working on converting my charter oak 12Z mill to cnc for many years now. When I started, that was pretty much the only way to get a cnc mill in that class short of buying an industrial machine. Today, I feel that would be a mistake. There are several cnc machines already ready already, so unless you really want to learn from the process, it is IMO not worth the hundred plus of hours to convert a bed mill. I'm pretty sure that without including labor I have spent as many dollars as I would to now buy a turn key machine.
I will say that while I'm no fan of CNC on hobby machines, the 12z was the first bed mill I owned that I considered large/rigid enough to do it. Got to visit with my old mill a short while back and the first thought that came to mind when I saw it was that I'd forgotten just how big those mills are. The table is larger than the mill I have now.