[Pursuivant]

I'd go with J-aircraft, since that forum has some serious Japanese aircraft geeks, and the posts cite high quality reference books as sources. Additionally, some of the posts are from people who have written books on the weapons and aircraft in question.

The Military Factory site doesn't offer any reference materials as sources, so it is inherently unreliable.

But, it appears that the Ki-45 was fitted with a variety of different weapons. Just because the J-aircraft forum is better sourced doesn't mean that it's a complete discussion of the topic! So, both sites could be right.

Rene Francillon's "Japanese Aircraft of the Pacific War" has the following info, but it's a bit dated:

Edit:

Ki-45 KAIa heavy fighter/strike fighter - 2 x 12.7 mm Type 1 MG in nose, 1 x 20 mm (Ho-3) cannon in ventral tunnel, 1 x flexible rear-mounted 7.9mm Type 98 machine gun.

Ki-45 KAIa - Experimental/Field Mod Night Fighter - 2 x 12.7mm Type 1 MG in nose, 1 x 20mm (Ho-3) cannon in ventral tunnel, 2 x 12.7 mm Type 1 MG or 2 x 20mm Ho-5 cannon in oblique mount. No tail gun.

Ki-45 KAIb - Heavy fighter/strike fighter - Late production aircraft had uprated engines (Ha-102). 20mm (Ho-3) nose, 37mm Type 98 ) ventral tunnel, 7.92mm (Type 98 ) flexible rear gun

Ki-45 KAIb - Experimental/Field Mod Night Fighter - As above but 2 x 12.7mm Type 1 (Ho-103) MG mounted obliquely upward. Fuselage gas tank removed.

Ki-45 KAIc - Night Fighter - Ha-102 engines, 37mm Ho-203 cannon in ventral tunnel, 2 x mounted obliquely upward 20 mm Ho-5 cannon. 1 x flexible rear-mounted 7.9mm Type 98 machine gun. No armanent in nose because centimetric radar in plexiglass nose was to be mounted there, but few were actually equipped. No rear MG on late production aircraft.

Ki-45 KAId - Anti-Shipping - 2 x 20mm (Ho-5) nose, 37 mm (Ho-203) ventral tunnel, 7.92mm (Type 98 ) flexible rear gun on early versions, not retained on later production.

Ki-45-II projected development. 1,500 HP Mitsubishi Ha-112-II engines = redesignated Ki-96.