I don't know if you ever came across the late great John Stevenson? He was a brilliant practical engineer with a business in Nottingham IIRC - one of his activities was refitting university CNC machines with modern controllers, as the mechanics of things like Boxfords and Denfords are generally excellent but the controllers outdated. He recommended packaged controllers like this:

https://www.ebay.co.uk/itm/275171431...Bk9SR5a8ytmAYg

I believe they are available either as complete packages like that or just the controller, or probably anywhere in between. The motors on your machines are probably OK but definitely worth upgrading to modern drivers with microstepping etc. This thread:

https://www.model-engineer.co.uk/for...?th=120519&p=1

...over on the ME forum contained a lot of discussion and good advice from Sir John.

If you go the PC route I suggest you avoid Mach3, it hasn't been maintained for something like 10 years and any bugs will never be fixed (even though you still have to pay for it!). Mach4 is reputedly much better and is actively maintained. Other packages that are highly regarded are UCCNC (from CNCDrive) and LinuxCNC but the latter has a steep learing curve! A good supplier in the UK (if you are in the UK) is CNC4YOU in Milton Keynes.

Having said that I converted a Denford Novamill using Mach3 and built my own control box, also a Myford Super7. But that was 10 years back, I wouldn't choose Mach3 again.