I'm thinking about writing a timeline, and one of the key points would be China and North Korea cooperating more closely with the Soviet bloc. I'd like to have an explanation beyond a handwave for this level of cooperation, and one of the ways I figured this could be achieved would consist in those two countries joining COMECON a bit before the Korean War. If there are reasons why this can't be done, tell me now so I can either figure some other reason out or try a different TL.
I can offer some perspective on China.
There was always a lot of bad blood between Mao and Stalin. This goes all the way back to the 20s and 30s. Stalin had favored the Koumintang rather than the Chinese Communist Party, and most of the Soviet aid had originally went to the Koumintang. Stalin wished to bring China into the Soviet orbit this way, going so far as to use the Comintern to mandate the dissolution of the CCP into the Koumintang, and continue to support Chiang during the Chinese Civil War.
This mistrust continued when Mao came into power, and Stalin still was less than helpful to the Chinese. The real breaking point came in the Korean War, when Stalin refused to support Chinese action in the war beyond a tiny token level. Mao saw the Korean War as the beginning of a global revolutionary war against capitalism, and Stalin would entertain none of this.