Thanks for the advice Gnasape. After musing over it I think I will merely wait for the rule set of the new Axis and Allies coming out in August. I can sub the classic battleships, as you advised, as cruisers and just use my current board with no need for alteration.
The game might be interesting with more territories to play in, but the game seems to take a long time to play as it is, so perhaps I will save a larger map for another time.
Thanks again.