In order to overcome the firepower that is the weak point of the Hayabusa, this prototype retrofitted 20mm cannon 2. Therefore, a big bulge is attached to the front of the cockpit. In addition, a part of the rear of the fuselage has also been made of wood. However, it ended in the prototype without being adopted.
Hi! The Army Type 91 fighter prototype and early production model. Almost same scale.
I can see rather large difference between these aircraft. Perhaps these difference is from No.5 prototype.
Source : as usual.