@moralecheck:
I wonder if simply requiring Japan to maintain a garrison (of x units or ipc value) in Manchuria, Korea and maybe Japan itself to watch over the the Russians would do the trick (no actual russian units would be required). Failure of Japan to maintain this garrison would be a NO for China, unless Japan loses those tts.
That’s actually a very good and simple solution! Historically they did keep the Machukwuo army in Manchuria throughout the war to guard against the Russians. Making The Japanese keep x IPCs worth of (land) units in certain territories could indeed make a big difference and solve the balance issues in Pacific40!