Not too hard to build a new controller, yes, you do appear to have the "Big Black Box" missing that has all the Motion Control system, power supplies, stepper drives and various fuse holders and relays etc, all the bits required to make the machine move
OK, you will need a decent size cabinet to house all your bits and pieces for starters but that actually may be the last thing to buy, get everyhting else first then you will know how big a box you need
A computer, couple of options here, either an outside free standing PC (There are some Quad core PCs on Ebay for around £90 that will do the job, or a smaller box inside your big one that you can fit a small modern Motherboard and SSD (Solid State Drive) inside, that way everything is in the main box.
A suitable power supply for all the control equipment (Motion Control Card, Relays etc) usually 24Volts x 2.5 Amps will do it.
Various relays to switch on/enable stuff like the Coolant pump and the Spindle drive. Not expensive
3 x stepper drives one for each axis and a power supply for them, again not expensive
A motion controller, a pretty good one is the CS Labs CSMIO IP M which is a relatively cheap industrial strength controller that uses 24Volts control voltage so is better for reducing any interference and the controller connects to the computer via Ethernet (CAT 6) cable which gives a fast connection speed and also is virtually interference free.
Some control software like Mach3 or Mach4, I have used both and I have found that Mach4 which is the latest and has been developed for Industrial use is the better of the two, difference in price is only about $21 USD.
As you have an Automatic Tool Changer on the machine there are again a couple of options, if using the Mach3/4 software you can write or get from the Forums a Macro (Small program) that will step the ATC to the tool required, or you can buy a smal PLC (Programable Logic Computer) that you can use to operate the ATC, a good little inexpensive one available from Radio Spares (rs-online) is the BARTH STG 600 which is about £90 on a next day delivery, you can get all your relays, fuse holders etc, etc, etc from them as well, I use them all the time
You will also need a drive for the Spindle Motor, on the Triac that is usually an SEM DC Brushed Motor and the drive that Denford usually fitted for that motor was a Sprint Drive from Sprint Electrics, they still make the drives in a more modern format and they are properly Isolated unlike the older ones, I bought one earlier this year for a Triac direct from Sprint Electrics and it was only about £200 if I remember correctly, I can send you some photos of the one I did from scratch and of one I am currently updating/upgrading to modern electronics and Motors etc !!
If you want any help with this project then fire me a PM via this message board and I will let you have a `phone number and I am happy to chat !!
P.S. A tip, please reduce the size of the images you upload, it is a right pain scrolling sideways to read stuff
Hope the above is of some help to you ! !
I have done a full control system on a Triac from just the bare casting, took a while, months of a job, nice Winter project for you