Hi Nigel,
Great piece there, and yes it was common to see what I call AGA barrels used in this way.
Often they were a personal choice, but I did see a numerical seqence numbered rifles once, all of which had those barrels fitted, so they must have done that for a special role one thinks.
The 5A PH MKVII sight always faired well on the SMLE and you can imagine with BSA just up the road, both companies often worked hand in glove to achieve the very best for the services! I have fired, very accurately an SMLE with the 5A fitted at Warminster many years ago, and I am sure Peter L might reflect if its still in their collection there, brillinat little sight.
PH foresight covers and the good old "Flanders Flaps" were often constructed by PH during WW1, due primarily to the severity of trench warfare and the incessant mud they had to endure as front lines moved back and forth, but few records remain of the detail on their design, albeit, I did put a drawing up on here a few years ago which I can not find now, probably dropped off in the ether lol!
Yes the two BA screws did exactly that, held the trigger guard in a firm position. They look like they have taken some beating with a blunt bladed screw driver over time.