Ok then you cant use them, unless that is they have dual contacts (Normally open and Normally closed) then you could run the unused ones to Mach, failing that getting some optos and using them may be a good choice, not a hard thing to do and very accurate if you can keep them away from coolant. I think however your machine must originally had home switches so unless they have been removed by the person who did the retro it may just be a case of wiring them to Mach.
Or of course you could do it Terrys way and locate some feature and take note of its coords then if you loose position touch off it again and enter the values direct to the DRO.
Hood