Nice find Lance. To be honest, I think she's what I would expect from a mid (ish) 1943 conversion. The rear sight, although a SM43, which is what you would expect, could be a replacement which by chance was made by Singer in the same year as the rifle. This would explain the lack of the 'S' on the cut-off block. However, the markings were not religiously applied as per Peter's book until later 1943 anyway, so we'll probably never know for sure one way or the other - the rifle could just as easily have left the BSA factory wearing that rearsight. Most of my 1941 to early/mid 1943 rifles have lacked the sidewall 'T', & those that I've had that possessed one I suspect may have had it added after the event by a judicious armourer. So, the lack of the sidewall 'T' on an earlier converted rifle does NOT necessarily mean it was a 'less telescope' rifle, & I'd lay odds yours went out with its contemporaneous Mk1 scope when it left H&H at the time. Incidentally, I think after writing the 4T book, Peter came across some documentation that suggests that the previously supposed attribution of 'KL' to Kershaw is not so, but is in fact 'Kodak Ltd', so your rifle originally bore a scope made by the camera people!
She's nice. I'd definitely give her house room!