Hi Eddie,
I have been looking for one of these sights for years. There were two types of PH aperture for late pre war BSAs. One where you had to cut some of the stock to make it fit and the other, which fitted directly onto the stock. The Sprawson would also be very desirable - he was a fascinating individual. I have a little information on his air rifle shooting career, which I have included in the manuscript I have been preparing for years.
I recently bought a Haenel 33 'Senior', which still has the original 8 shot mag. The prewar 8 shot mags were intended for this rifle only and had the magazine notch machined further down than the 6 and 12 shot mags. For this reason post war mags will not fit the Senior unless a new notch is machined. Sadly my original mag was damaged but my friend Paul O'Donnell adapted a post war 8 shot and I have been enjoying myself with the Senior ever since. The Kynoch shot mentioned in the catalogue is 4.45mm rather than the post war 4.4 mm and some reviewers, such as one from July 2010's Airgun Shooter suggest the rifles do not like anything but 4.45mm. That has not been my experience though, as my Senior digests 4.4mm ball without jamming.
Sorry, seem to have gone off at a tangent.
Kind regards,
John