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just looking at the early war RKKA Red army set and see that many wear the pitloika or side cap , which can be used as Mongolian troops in the 1939 Nomonhan /Khalkin Gol campaign against the Japanese.
You are probably right about the cap band.The uniform was the same as the Soviet fall collar M35 uniform. The Mongolians had the larger M22 style badges, insignia especially on the cuffs and these were of course to a Mongolian design. The pilotka was identical to the Soviet version. The Soviets also wore the M38 Panama hat and the light summer uniform in the summer months.
I would be more concerned that they don't have oriental features. The Pegasus Russian WWII figures sand and glue well and I have made North Korean and PLA from them. The legs can be shortened to give them an oriental stature to match the Japanese. Having said that some Manchurians can be over 6 foot tall.
About time somebody did some WWII Russian troops with Asiatic features.