Looking for an older CNC mill to refurbish/retrofit

I'm starting a search for an older CNC vertical/knee mill for my home shop and thought I'd introduce myself and ask for advice before buying something.

I'm currently looking at an older Wells-Index CNC mill, but I'm not committed to a particular machine yet.

My objective isn't to gut an old machine and replace everything. I would like to retain the original mechanical and electrical hardware where practical—including DC servos, feedback devices and possibly the servo drives/amps. The obsolete CNC control is another matter, it's a 70s vintage Bosch and going in the dumpster (or I might make it into a coffee table .  Thinking about LinuxCNC/Mesa.

Typical work will include aircraft instrument panels and other aluminum parts, but I also want a real mill capable of occasional work in steel.

I'm comfortable with electrical/electronic troubleshooting, software configuration, and I can spell Linux. My main concern is driving the old servo amps and are they serviceable and/or repairable.  I think the old brushed servo motors are OK. 

I'd appreciate advice from people who have restored or retrofitted older industrial CNC mills: What machines from this era are worth saving, and what should I inspect before buying?

Thanks in advance
 

Aircraft Instrument panels are larger than most knee mill tables.
Bridgeport Series II Interact have larger tables. Older Series II units have steppers.