Why a British super-cruiser would likely use 14-inch guns

Could Britain have armed a Second World War super-cruiser with 13.5-inch guns?

Probably not; six 14-inch guns in three twin turrets would better match the weapons then in production.

Britain lacked active 12- and 13.5-inch production, while twin 14-inch mountings could be derived from the King George V program. A Renown-like arrangement of three twin turrets and six 14-inch guns is the likely result. Reusing Iron Duke's 13.5-inch turrets is a poor alternative because the ship still served as a gunnery-training platform and the late-1930s survival of suitable stored weapons is disputed. Whether the new ship is called a battlecruiser or super-cruiser would depend chiefly on its scale and protection, since no intermediate calibre was readily available.