Don't work like that Killer300; "If the shoe don't fit, you can't shoehorn her".
Stating; "I want this history/world." while at the same time failing to recognise that there might be many issues with it that prevent history being like that, is the height of naivity.
All we can do is pick a POD, and then chunk through the plausible repurcussions of. Trying to retcon 'a present' with a past is highly contrived to making it total fantasy rather than plausible pertubations to the timeline we know.
That said; "Aliens landed in 1900 and placed icesheets over Russia and the US. Just them, no other states. Then left. ...go figure ¬.¬"
You see my point?
Okay, three problems with this.
1. I'm further explaining PODs I stated IN THE ORIGINAL TEXT. I already said the US had a more chaotic Great Depression, and that the USSR states isolationist.
2. I do recognize there are problems with this scenario, otherwise, why would I have added that?
3. Neither the US or the USSR are destined to be superpowers. Brazil, despite having massive access to resources, and lots of manpower, still isn't a superpower. For the first two, both had help from a World War to get that status. Take away involvment in that, and you don't get the set of factors that transform them into superpowers, which here is that they project power beyond their immediate neighbors.