I bought a tungsten carbide drill bit and tried to drill out the sheared HSS bit in the sheared disk bolt today.... it took around 3 or 4 seconds for the drill bit to bite and the stuck bolt shaft wound straight out of the wheel. Result!
In fairly typical sods law style it was the same day that I completed painting the replacement rear wheel:

so now I have a spare pair of wheels that I only really bought because of the sheared bolt. I'll fit them to the yellow bike when the weather improves. It means that I have a brand spanking front BT45 tyre to sell that I no longer need.
The radiator on the yellow bike has suffered the usual lower corrosion and the bottom mount is no longer attached. I bought yet another radiator from China which, amazingly, fitted inside the Honda cover! The paint finish on it was terrible however so for the first time in my life I took some sand paper to a brand new part and prepared and painted it:

I'm waiting on the latest genuine parts order delivery for new headlight bracket mounting rubbers before front end re-assembly can begin.