The real-life armament of the L,M destroyers (apart from four Ls with 4x2 4"HA) was the 62pdr 4.7" L50 in the MkXX weatherproof gunhouse (not turret, there was no rotating ammunition feed below deck) which gave an elevation of 50 degrees. These look
very like the mounts depicted above on Musketeer.
http://www.navweaps.com/Weapons/WNBR_47-50_mk11.htm
The turret version of the 4.5" BD (elevation 80 degrees)was as shown on Matchless 1957 above, but was fitted to the Battle class. Matchless never had them.