Directly after WW2, the USSR had a bigger army than all the other armies of the involved powers combined. In 1950, they would've still held an overwhelming advantage and could have taken Western Europe with relative ease. Korea would also be Soviet territory and America would be helpless until they did make nukes.
Yes, and that massive army is going to have its combat efficiency drop dramatically when its no longer receiving a constant influx of American made trucks, grain, boots, clothes, and rations; all of which the soviets lack an immediate quantity to produce on the scale required in such a situation.
Also, the U.S. would have a decided advantage in strategic bombing through the mid 50's, with the USSR lacking sufficient high altitude interceptors to really prevent the US from raining bombs down on soviet military installations.