This is like gold! Many thanks for your replies.

A DAO hammer - Ruger identifies hammer assemblies as factory fit only. It's the weekend so I'll ask here whether the DAO hammer is still available from Ruger for SP101? If it is, will they replace the existing hammer, or will they return the original to become a spare?

I have seen semi-DAO hammers on revolvers where there there remains sufficient metal to allow very-deliberate-only single action. Were DAO hammers unavailable from Ruger, are there any suggestions for who might be able to alter my hammer?

Regarding chamfering chambers, I load single cartridges. Would such loading profit from chamfering?

And now the puzzler. I have small hands. I find my OEM grip too long. When I do my slow and deliberate practice draw and fire at home with snap caps, and at my private range, too many times my grip is incorrect for me - that is, I don't take control of the revolver grip the same way every time. A grip closely emulating my (given to a friend) S&W 640-1's OEM boot grip would be a major improvement, I think. But who makes them for SP101s? of wood? without checkering?