Tony,
The 6" guns fitted to M33 were 45 calibre Mk XIVs - a much later and longer gun. I haven't been able to ascertain what guns are fitted to her now, but they are definitely longer than 26 calibre.
26 calibre MkIV/VIs were fitted to: RN cruisers of Orlando, Mersey and Archer class as well as Marathons; Jap cruisers Uzumin, Unebi and Naniwa class and a converted Peruvian merchantman called Lima; RN battleships Sans Pareil, Victoria, Imperieuse and the Queen Elizabeths - although this later use seems unlikely.
Rick