Much credit for the diagram should go to "Slotalot" and "Operator Bell" for their (much) earlier help & guidance.
I have marked some of the wiring (eg Relay RL5) in red to denote how it is different from the "standard" Roto Pool (Mk2) diagram. I am not yet comfortable/happy with RL5 being wired to the ac side rather than the rectified dc side but that's how I think it was wired????
On the lower RH corner of the MAIN schematic, I have shown the switching arrangement for switching the payment from 2d/2d/2d to 2d/4d/6d. It is accomplished with a fixed (to the cabinet back board) 8-pin plug and a removeable 8-socket (Bulgin-type) socket. The socket has had the plastic "key" cut/filed away so that the socket can be fitted to the fixed plug in (at least) 2 different orientations...(2d/2d/2d and 2d/4d/6d). Note that the moveable socket has internal wiring!
I have followed Slotalot's format though my + and - dc rails are inverted with respect to his diagram for some reason. The electrolytic capacitor across Relay 1 contacts will need the correct polarity. Other than that, I'm not sure it really matters.
I'm hoping to complete this as an electrical project by Christmas now.
Hope this helps others.