I really see the US not getting involved in a war with Japan in this TL all the things that pitted the US and Japan in this TL don't exist no rape of China, etc. so their would be no need for the embargo as China is capable of handeling its own buisness with its own large army and navy. So the Japanese will have a constant and regular flow of American raw materials and the Chinese will have a constant flow of purchased American weapons and technology. The British would also be quite content with dealing arms and resources to both sides, and with that in mind I don't realy think the Japanese with a stong China still in the fight will risk sending resources needed to fight a strong China to an ultimate doom against those who are selling them arms and resources.