This is a really lovely story. The result of your lads work is fantastic. Graduate from the University of Life. The colour of that CB is just right - yellow with red trim. Beautiful.
I have 2 lads, now 22 and 27. Absolutely no, none, zilch, zero interest in 2 wheels - full stop.
I tried, and I tried, the workshop was always open, tried to show them mechanical things but all fell on deaf ears.
I have a workshop full of hand tools, even down to LH thread BA taps (never used them funnily enough), power tools, machine tools, materials, plenty of space for projects.
When I pop my clogs, they will have to clear that out and will not know what any of its does or is used for and hopefully they will not just dump it. In fact I going to write that in my will. Workshop contents must be given to model engineering society, cycling club, vintage motorcycle club etc, etc.
So, I'm really happy that your lad has taken an interest. Hope he keeps it up.
The photograph of the Cwmcarn Paragon interested me. How simple was cycling then, if a little less colourful though. No padded bib shorts or lycra shirts, bobble hats and work jackets/blazers will do fine.