Try turning countries like Portugal, Spain and Turquey as City-States. Egypt, by that time, was controlled by the British, the same happening with the Suez Channel. Australia may be a playable power allied to the British, representing by the Anzac, the commonwealth powers in Oceania. It would be marvelous also to figure out a nation without lands, representing the armies from the countries occupied by the nazis who refugeed in Great Britain after Dunquerne.
Try to give China some restrictions, as beeing unable to build tanks or airplanes since it was not industrialized. Brazil entered the war lately, so its interesting to begin with only a few built defenses.
It would be wonderfull if the airplane could reach in a single fly from Natal to Morroco and emulate the strategic importance of the northeasten part of Brazil.
If possible, replace some obsolete resources as masonry with others, like rubber. It would be interesting if iron is needed to build tanks and sea fleet.
Figure it out different wounders that make sense during the War time. Replacing Wounders such as the "Mausoleu of Halicarnassus", the PYramids (it makes no sense its special effect in 1939 with others like Hollywood, The Quinquenal Plans, The New Deal or the Nuremberg Festival should also add some flavour.
The suggestions I give are based in my experience playing Axis & Allies boardgame and with my experiencing mod a WWII scenario for CIV II. I'm terrible with programing, so I try my best suggesting nowadays.