Main problem with doing an early China vs. Japan setup is a SERIOUS lack of aircraft. We don't have ANY Japanese fighters appropriate for the period (Japan did NOT use the Zero in China until sometime after the AVG was absorbed by the USAAF. We need the A5M, Ki-27, and Ki-43 for later, during the AVG-period. Additionally the G3M would be the most representative bomber of the time, although the G4M appeared then as well). Allied aircraft aren't much better off. There were a lot of lend-lease aircraft, so the P-40B would work, MAYBE the Hurricane Mk.I, (someone can probably correct me on that) but we'd also need aircraft like the P-36 Hawk, even the Boeing P-26 and some biplane fighters.