Why not move the third turret aft?

Could the third turret be moved aft to make a conventional layout?

Not without major penalties in insulation, machinery layout, weight distribution, and usable internal space.

Moving the third turret aft would require far more than a revised deck plan. The machinery would need to move, with insulation between it and magazines at both ends. The change would disturb the ship's balance and create internal spaces that were harder to use. Keeping guns and magazines together, apart from boilers and engines, avoids those penalties.