I though Eelfish was a Balao, and Mako was a Gato.
At any rate, in 1945 you can set up a Gato or Balao with dual 5 inchers, and as you know, the AA guns you can configure how you want.
I seem to recall someone fiddling with the availability dates for dual 5 inchers. Try the Search feature in the mods forum and you will likely find it.