Why a King George V hull is the wrong large-cruiser base

Could a twelve-inch-gun King George V design serve as the basis for a large cruiser?

No; the required cruiser hull would be different, and Vanguard or Lion would be a closer starting point.

Changing gun caliber does not automatically convert a battleship design into an effective large cruiser. A large cruiser needs a hull shaped around different speed, weight, and operational priorities from the King George V class. The range of speculative twelve-inch armaments also makes it impossible to treat the proposal as one settled design. If a British capital-ship hull had to provide a starting point, Vanguard or Lion would be a closer conceptual basis than King George V.