Just to kill this one.
Many thanks to Quantum who supplied a photo-copy of a circuit which arrived this morning. I can confirm that it is the correct circuit and one that I built successfully some 40 years ago. It will be interesting to see if a reconstructed set works as well as the one I built all those years ago.
The young lad that want's to have a go at building it is looking forward to getting started so I'll sort some bits out over the next few days.
Thanks once again. What a great place this is!
Rich.