Well, snorkle aside, it's all possible. At the very least, though, we need the Tang class and the numerous GUPPY variants for the Americans and for the Soviets we need Whiskeys and either Tangos or Foxtrots.
I don't think nuclear boats are out of the question either, so long as they're from the 50s or early 60s and we fix the couple bugs with the one we have. On that note, the Skate would be the perfect counterpart for the November. USS Skate was commissioned in '57 and the class is basically a downsized Nautilus with the re-addition of 2 stern tubes. And if missiles can be implemented then the Hotel class would be great for the Soviets and the Halibut or Growler for the US.
Anybody willing to start modelling any of these?