I seem to recall in one of my Canadianicon manuals from the early post war period that such a conversion was allowed, that is the rear action body could be drilled for one screw hole to allow use of either the No 9 (C, F, G versions) sight or the No 5a sight. So that formate was allowed in competition atr least until the late 1940s in Canandaina SR(B) competition. I am pretty sure this was allowed at least as late as 1953. I have a 1967 Connought Bible at home I can check if you like to see if such a modification was still allowed.

Given such was allowed by the rules and was set up accordign to the rules, why would one change it?