Triple Entete:
France* - 186
Japan - 169
Manchuoko - 45
United Kingdom* - 284
Total: 684
Neutral:
Soviet Union - 359
United States of America - 800
* - not formally involved in war at this point...
There are a few things to enter into consideration at this point too:
Japan can freely trade with her allies France and United Kingdom as they have control of the seas. Chinese trade with Italy and Germany have to be rerouted all the way to Afghanistan and Iran through to Turkey to the Balkans and finally into Germany/Italy...
GDP does not necessarily equal military production, but it's a useful indicator of relative economic strenght. Japan/Germany/China are authoritarian regimes that have moblized for war and are much quicker in converting from GDP to Military Production.
China trades freely with both the United States and the Soviet Union, both nations want China's rare metals such as tungsten as well as Chinese silver dollars. Both are willing to furnish industrial and military equipment as well as 'technical assistance' in exchange.