Yes, I remember that grey single and twin screen wiring in the SSL 651 centre section as I worked there at the time (1980-87).
The grey cable was an unknown make but probably bought from RS Components then.
Since then, many more makes and types have been available including Mogami, Van Damme etc so, as a long time installer and wiring person since 1987, I would suggest Van Damme as a default, depending on which Country you live in. It is popular in the UK but other makes are used in other Countries in Europe and the USA etc.
Hope this helps a bit and rewiring any part of the 651 centre section is a complicated task, especially if you have to re-pin any wires into the two Mrac connectors.
As a wiring person, this would be easy for me but, good luck with this task.