The 6 free infantry can be deployed in any original Russian territory in their eastern provinces (i.e. the two Pacific boards) at the beginning of Japan’s Combat Move when they declare war (although I don’t know why Japan would declare and not attack).
But it is so interesting that Larry left it up to the players to decide what the terms are, so it can be different every game (though a standard will probably emerge, especially for tournaments). Heck, you can choose off-the-board terms if you want, I guess: if Japan breaks the treaty, they have to take a shot of vodka, and if Russia violates, they take a shot of sake, thus impairing them for the rest of the game.