So that means those two should be able to carry canons aswell and participate during shelling.

Heck it would be cool if their kai ni allows them 5 slots to use those

Since both Akagi and Kaga were battleships converted to fleet carriers, they had some design flaws: one of them were the casemated 8-inch guns mounted near the waterline at the stern.

These guns served no practical purpose whatsover: they couldn't be elevated enough to provide AA fire and since carriers rely on planes for attack their targets and are lightly armored (so they can carry more planes, fuel and ordnance) they were never used in combat (as far as I know).

The 8 inch guns were the remains of the times they were designed. Akagi, Kaga, Lexington, and Saratoga had 8 inch twin batteries on commission. These were in case they ran into the opposing fleet's scouting cruisers while scouting for their own fleets. As scouting was the job of the aircraft carrier in 1923. The airplanes they would carry at the time were probably not considered enough to actually threaten an enemy cruiser when these four ships were designed.

Later, as airplanes got larger and could carry larger playloads, it was established that they would be the striking force as well as the scouts. Kaga and Akagi lost theirs in the 30s rebuilds, while the Lexingtons didn't lose them until the war started.