No, no, you're quite right. The original limit was at -5 degrees. When it came time to modernize their ships, the Japanese took a unique approach to increasing their gun elevation; they lowered the trunnions and working platform. This allowed them to get 43deg elevation, but it cost a couple degrees of depression, which I doubt they missed.Cannot read Japanese, it looked like five degrees on the drawings. My fault.
If you don't mind, I'd be interested in any material you have on the original design. Could you send me an e-mail, my screen name @alltel.net ? Thanks much.