Futurewar, I don't think the guns could reasonably be that long. It just doesn't make sense.
If I were you I'd consult some of the drawings available in the archive for a way to tone this ship down and get it within reasonable limits - I'd start by going over to a 2-1 turret configuration to begin with. As it stands this ship is just impossibly big.
That said, if you're going for something that's totally implausible, I think this ship would be well-suited for the "LSBBT" - the Landing Battleship, Tank. Add some treads on the bottom of the hull and some bow doors and this ship can then drive up onto the beach and disembark an entire battalion of troops with supporting armor. It can then wheel itself back into the surf, retract the treads and sail back to the troop ships to pick up more assaulting infantry.
While you're at it, I think it could benefit from some similarly-modified midget submarines, which could be deployed before the initial assault to recon the beach head. Equip them with a VHF radio and they can call in the enemy disposition at will.