I have got my Dolch PAC-62 keyboard now, with "RJ-cable". There is no connector on the outside of the case, but there is a 4P4C-connector mounted to the circuit board
inside the case! This is the same connector as on a typical telephone handset, and the cable is just as short and coiled as a typical handset cable.
Most likely, I will need only to make myself a new cable to make it work with my PC. I have just to find myself an old phone ...
Mine has got a ISO layout, which is what I am used to. The switch PCB and controller PCB were were both made by Cherry.
I noticed that the location of the Alt Gr key is the same as on a PC/AT keyboard with windows-keys, which means that my muscle memory for typing special characters does not have to be re-learned.
The space between Esc and F1 is smaller than on most PC keyboards, but there is no space between left Control and the Alt key which aligns it against the F1..F4 keys just as on a typical PC keyboard. This is nice for those of us who have established muscle memory for those key combos under Linux to switch console/workspace.
Smells nice too.