conversion of old nc to new drives

I have an older Tree Journeyman two axis knee mill that was set up to take some sort of cassette reader using somesort of magnetic tape cassette instead of punched tape. THis may have been a common drive at one time but it is the first one that I've seen. Anyway, the boards are faulty and I get a malfuntion message on the screen. I've checked with the service guy Tree recommended to me and he told me that the boards are not available. He did how ever state that I could conver it to using the x & y feeds as simple power feeds to use the mill ans a standard manual mill if I desired. I would like however to see if there is anyway to conver this machine to operate off a PC and still use the factory installed x&y axis motors and encoders. Can anyone help me with advice on how to do this?

Trusting HIM,
Steve Rollert
keenedgeknives.com
doveknives.com