It is debatable as to whether or not plans for Unzen actually existed due to the destruction of sensitive information by the IJN prior to surrender. What is known is that a triple 203 mm gun mount, never actually mounted on any Japanese CA, was considered for eight ships planned under the Sixth Naval Armaments Program but no other information has survived. Certain postwar sources such as Japanese Cruisers of the Pacific War and Uncompleted Fleet Plan - 1917~1950, from where the Unzen/Zaou design was based from, are informed guesses.
However, more information surfaces that the Zao-class cruisers are confirmed to be "Type A 1941 Heavy Cruiser" projects in which is derive to the later Mogami and Tone-class cruisers, armed with a Triple 203mm experimental mount and Experimental Torpedo mount.
