OK: more confusion to be added to the fray. Not exactly 10m rifles but Original did 'Target' versions of the 35 and 50 models, equipped with dioptres.
I had a chance to look at their dioptre fittings this afternoon and guess what: they are all different and no way will any fit onto an LGR; indeed they will not be transferable from one model to the other. The ones with the large 'thumb wheel' fitting clearly fit onto dovetails with cross grooves to allow fine tuning of the position. Another version can be adjusted for elevation but seen to be screwed to the cylinder.
I wondered if a HW dioptre from a HW57 might fit, but no, the rails may fit but the fact that the bottom rear of the sight is below the cylinder means the LGR cocking lever cannot operate. Maybe a riser block would help but it would clearly be a bodge and so I consider it a 'no go'.
Clearly a lot to learn ...
Cheers, Phil