1986 is a pretty old machine. A quick call to Thermwood would tell you if parts were available.
I doubt you could upgrade the old control to work with eCabinet software.
I don't know how complex the control in that is, but you could always rip everything out and build a Mach3 based control, or one of the more expensive controls. I'd think the important thing is that the screws and linear rails are in good condition. Motors and electronics are relatively easy to replace. The big ticket item would probably be the spindle, which I'm assuming is missing or in need of major repair/ replacement.