From memory that looks right. I had forgotten about the top pcb. It is lying around somewhere. I made a replacement board for the one in the middle, using some of the original components on my replacement. I will still have my original track layout somewhere on my computer and I think I have a couple of the connectors. I'll check lunchtime.

'would it be practical to get the mill running on mach 3 and move onto these later?'
That's the way I did it.

To run the button interface you will need 'keygrabber'.
It is all a bit shrouded in time, but all available somewhere.

Dave