trurle
Banned
Japanese were buying a lot of military hardware from UK, Germany and France before ww2. It might be plausible for them to take a look at the Somua tank, then on the Pz-III, then on the Stug-III, and decide to combine the best features in a tank and in a self propelled SP gun for direct fire.
They can take a look at Birch gun, and un the French 194 mm SP artillery, and go with a SP artillery piece of their own.
A SP AAA, mounting 2 x 20 mm might come in handy, both for AA duties and for direct fire against infantry and light obstacles, much like the Soviets used the Shilka in Afghanistan.
Japanese had the designs you mentioned.
Type III Ho-Ni was an analog of Stug III was a high-performance 75mm universal SP gun. Also, the Type 98 20 mm AAG Tank (To Be exact, Ho-Ki variant) was the 2x20mm armoured vehicle. Unfortunately, with US phasing out bombs in favour of HVAR rockets, none of these designs (or any plausible alternative to them) was survivable. 20mm AA guns were simply out-ranged by HVAR, and tanks top armour was easily pierced by earliest semi-HEAT HVAR warheads.