The original designers made a mistake. IDC header cables carry pin 1 to pin 1 for stack of boards with the connector on the same edge, but not for two boards facing each other. That is fine when using vertical headers, but right-angle headers bend to the right, by convention and to avoid having to make two variant headers of each right-angled headers.

This would be fine if the designer had designed the Speculator and Silicon Disk to be "upside down" in their box, but they are not. Therefore pin 1 of the Einstein goes to pin of of the cable, but the Speculator pin 1 goes to pin 60 of its connector.

The original system seems to get round this by cutting off the polarity bump on the IDC socket, which then allows the IDC socket to fit either way. 

We now have to make suitable cables for new kits.

Lee shopped around and found that it was cheaper to by ready-made cables then their components.

https://uk.farnell.com/w/c/cable-wire-cable-assemblies/cable-assemblies/ribbon-flat-cable-assemblies?st=2.54+60+ribbon+cable&range=inc-in-stock

The header-to-header cables have the headers in the same orientation. Fine if you accept cutting off the polarising lug at the Speculator end. There is also no way to add a 3rd IDC socket for a Silicon Disk.

The original system had the cable about 100 mm, or 4 inches. This is very short, to reduce signal ringing.

https://uk.farnell.com/multicomp-pro/mp012858/cable-assy-60p-idc-rcpt-rcpt-100mm/dp/4243759 (£3.32) is 100mm header to header.

https://uk.farnell.com/multicomp-pro/mp012774/cbl-assy-60p-idc-rcpt-free-end/dp/4243666  (£2.95  is 100mm to free end, which would allow tw IDC sockets to be slid on, in inverted fashion (pin 1 to pin 60).

https://uk.farnell.com/multicomp-pro/mp012775/cbl-assy-60p-idc-rcpt-free-end/dp/4243667 (£2.47) is 150 mm to open end but even cheaper.

https://uk.farnell.com/multicomp-pro/mc-254-60-00-00-idc/connector-rcpt-60pos-2row-2-54mm/dp/2843507 (76p) is a 60 way IDC socket. It makes sense to have two at the Speculator end, to allow for a Silicon disk in the same case.

So the cost of a cable would be about 247+76+76 = 399p.