We unplugged my "Heeksatrol" computer from the Bridgeport Series 1 and replaced it with a PC running LinuxCNC. In less than a day we had it moving the 3 axes, with very little work by us.
We copied some code to make LinuxCNC ask us to press a button to continue on a tool change:

 loadusr -W hal_manualtoolchange
 net tool-change iocontrol.0.tool-change => hal_manualtoolchange.change
 net tool-changed iocontrol.0.tool-changed <= hal_manualtoolchange.changed
 net tool-number iocontrol.0.tool-prep-number => hal_manualtoolchange.number
 net tool-prepare-loopback iocontrol.0.tool-prepare => iocontrol.0.tool-prepared

But we didn't work out how to make it retract up to our limit switch on a tool change, yet.