Does anyone know of any available adaptors to fit modern rear sights on to a BSA Martini Mk III ?

I have a Mk III with a Freeland sight on it which is pretty much useless. So there is the side mount for a PH25B sight and also the top mount for the Freeland sight. Could use either of them...

An Anschutz sight would just about slide on to the top rear mount but it needed longer bolts to tighten it, and even when it was on I couldn't get the elevation on it.

Alternatively, if anyone has a PH25B sight lying around they don't want, I'm happy to discuss new ownership!

Thanks.