Besides the gun you mentioned their is a the 3.9"/65 Type 98 Duals that are shortish range rapid fire guns (the D variant is stated at 1.7 sec reload) that have high damage per shell. Their are also the 3.0"/60 Type 3C Duals that are shorter range guns (45 degree golden angle is laughably close to the ship) but have the same reload as the 3.9" but less damage per shell.

Really using any kind of AA is mediocore at best as IJN until you get those delicious 4.7"/45 Type 10 Dual guns that snipe planes from far away. The 6.1"/60 Type 3 A's are also good on the mogami and fire similiar to the the Type D's you're using now.

I suppose you are on the Mogami CL/Myoko, trying to get some levels.

For mainly AA

I recomend those 2 x 3,9"/65 Type 98 D. I actually used them myself a long time ago while lvling my AA gunners.

Also those 5"/50 Type 3C D are a good middle way. They have same 38 degree golden angle as 2 x 3,9"/65 Type 98 D. It will teach you to snipe planes. Still they leave you with good anti ship dps.

The tripple 6,1 are for mainly shooting at ships, for wich they work very well. They have the longest range, but also longest reload. If you are good at sniping, these will work as well.

As always i recomend going for 3/4 AA shells, and rest heavey HE. This is the IJN CL/CA AA setup for GBs. For T slots go for HH.

Happy hunting.

Since the OP asked for advice. IJN  is worthy of DP gunners.  Take the time and lvl up someArmament sailors but delay class.  I delayed mine to lvl 80-ish and it was well worth it.

Why would you not get IJN AA gunner for AA ? That's the problem. If you have use the search function, almost everyone advise is to get AA gunner for IJN. Get IJN AA gunner and your problem solved. 

That's true but, using HH during that time is a viable option.