I might be able to help with some basic concepts here. I think the best way to go for the Western Allies (US and UK), is to create a two-pronged threat into Europe, in much the same way they did historically. The British should build a fleet (based around BBs for those invasion supporting fires), and park it in Z6. From there they can land in Nwe, Nwy and Fin (all typically weakly- or un-defended) while still threatening Fra and Ger (the 1st key). The US simultaneously builds a fleet (based around carriers and fighters cause that’s what they start with lots of). This fleet bridges from Eus to Alg, and streams troops into North Africa starting US2, while simultaneously threatening Fra and Ita (the 2nd key). The bridge can eventually be moved from Eca to Alg, which improves the US ability to strike Fra. The beauty of this two pronged approach is that the Italians are then forced to defend Italy and battle for North Africa (if they can) and thus are unable to reinforce Fra. This then forces the Germans to reinforce Fra, which draws vital ground troops (infantry–and they can only make 10/turn if they don’t build/capture any ICs) away from Russia. Simultaneously, the US and UK need to begin a combined SBR campaign against Italy, which should leave them unable to produce more than a few inf/tanks a turn. Coupled with this, the Russians need to build as many infantry as possible while conserving what they start with, and back them up with a few tanks or fighters for counterattacks and defense. With German forces tied to Fra and Ger, the Russian infantry stacks should be able to go toe to toe and grind down the German attackers.
My first couple turns look like this (in brief outline form):
R1 (5xInf, 3xTank)
Counterattack one of the NO territories if feasible to deny the Ger NO
Build a huge stack in Bel with all available forces (abandon Kar as it’s essentially lost anyways)
Screen the rest of the front with 1-2 inf per territory
Inf from Siberia retreat towards Mos, inf in Kaz and Nov move into China (slowing the Japs down will help hold Mos later)
UK1 (BB, CV, Tran)
Destroy Ger fleet
SBR Italy if possible (ie bmb isn’t needed for fleet destruction)
Any surviving Egy forces (tank and/or ftr link-up with 2xInf from Trj and the Ind defenders in Per)–this creates a big stack that can hold out for a bit rather than being defeated piecemeal
US1 (CV, bmb, tran, inf, arty)
2xBmb to Gbr
Surviving carrier/dd to Panama Canal with Haw ftr
Place fleet in Z10 along with Wus and Eus fighters
R2
depends on Ger/Ita turns
UK2 (depends on available money, but should be a fleet unit or two, a loaded tran or two, and an extra bmb)
SBR Ita
Land in Alg with fleet (no more Ita NO)
US2 (more fleet units, loaded trans and a bmb)
Land in Alg with fleet
SBR Ita
Move Pac carrier/DD to Z10
On round 3, the UK can move their fleet away from Z12 to begin my previously described threatening action (the BB will probably have to stay to provide backbone for the fledgling US fleet), but all the elements are now in place. When the 2nd US carrier arrives on US3, that should free the UK BB to go back to its primary task in Northern Europe. With all of Europe’s coastline threatened, you should be able to make a convincing landing somewhere (ideally you can get Fra, and then 1-2 punch it with the Allies) around Turn 5 or 6 (and Russia SHOULD be able to hold out that long!). Italy will probably fall the turn after Fra, as it should be at 10-12 IPCs after Round 2 while being hit with 3-4 bmb minimum. Once Italy falls, it almost doesn’t matter if Germany takes Russia, as they will be too far away to stop the UK/US bum rush into Berlin (8 production spots in Gbr, plus 6 in Ita, plus what the US can ship over in the transport chain) that will happen approximately 2 turns after that.
I have used this formula numerous times now and it is very effective, and the Japs can’t stop it (although I admit I’ve never faced the Polar Express, but it just doesn’t sound that effective on paper). By the time Japan is knocking on Moscow’s gate, the Germans will have more pressing problems to worry about in their rear, and the Commies should be able to turtle up against the Japs and wait for the cavalry (and/or the Ita/Ger demise)…
Hope this helps.