Would 5.25-inch guns fit the old hulls?

Would 5.25-inch guns fit the rebuilt Town-class cruisers?

Probably not in the proposed conversion, because their deck-penetrating mountings would require changes to a hull not designed for them.

The 5.25-inch option encounters the same installation problem as the 4.5-inch alternative. Its mounting needs to penetrate the deck. The old cruisers were not designed around that type of weapon installation, so it falls outside the proposed conversion.