Well after a lot of faffing around, I think I have sussed the clock repair technique but you will need a lathe.
Using the tried and tested method or separating the two main parts of the clock - a large jubilee clip around the stainless steel band and judicial levering of band at the back, the rest of the clock is fairly easy to do (assuming that the units work). Mine were working but paint was peeling and the dials were shot.
New faces from 750faces.com, new screws to affix from china (aliexpress) I used M2.5 and tapped the holes accordingly. Powder coated black bezel, re-plated the back part, a dollop of fluorescent paint on the needle and then a good clean of the other parts before re-assembling and then putting in the lathe with the jigs as per the pictures below:
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Then it was a matter of making sure the tailstock is locked hard against the rear 'cap' and then using a roller tool, the ring was 'spun' back on.
I'm simplifying things slightly but that is the general process. The rear nylon cap doesn't have to be so elaborate - it could be a bat held on by the captive studs but I used it as I was experimenting along the way. The trip arm was made using an M3 Left hand tap on some suitable s/steel.
In my euphoria of getting it to work I managed to affix the rev counter backplate the wrong way round!!!
So I'll be looking for another ring......
Let me know if you want more specific details.
Matt