I wouldn't waste any time on it just gut it.!!
IME These things are like a box of chocolates and no two are ever the same and you don't know what's been messed or what works or doesn't unless you have seen it working.

Fit 2 x new drives run it on Linux CNC with a couple of parallel ports using £5 BOBS and away you go. Linux CNC is far better for lathe's than Mach3 as it allows multi-count encoders for things like spindle speed or MPG's.
Now I'm a long time Mach3 user and some would say fanboy, so for me to say Linux is better is like pulling teeth with pliers but it's a fact. Thou it's got a bit of a learning curve it will be the better option than Mach3 and much cheaper.