Hey 321, those A6M's that have the A6M5 wing but the A6M3 engine package are actually very early A6M5s, not production transition machines. The decision to move from an exhaust collector to individual stacks came after the introduction of the M5 series ( I have forgotten where I got that tidbit of information but you can probably find it at
www.j-aircraft.com if you're so inclined). The A6M3, model 22 (enunciated "two-two" for those of you not familiar with Japanese zero model designations) means that for the A6M3 model there have been two engine changes and two airframe changes since the 12-shi (prototype). the model 52 had five airframe changes and two engine changes since the 12-shi, one of those being the shorter, rounded wing.
All A6M3's were built by Mitsubishi while Nakajima was still cranking out A6M2 model 21's (aka A6M2b). Both factories built the A6M5's but there are distinct differences between the makers that allow the easy identification and distinction between factories.
