Could a larger Arethusa replace twins with triple turrets?

Could an enlarged Arethusa design be built with twins and later receive triple turrets?

Yes in the proposed larger-hull design; the extra dimensions of La Argentina are used to explain how the triples could fit.

La Argentina was an enlarged development of the Arethusa concept. Extra length and beam made triple turrets possible. A similarly enlarged British hull could hypothetically begin with twin mountings and later receive triples. That accepted possibility concerns a proposed larger design, rather than a simple refit of the original smaller hull.