Here are some genearal thoughts in no particular order:
The most basic observation is that WW2 troopers did not wear armor. So, you could actually just assign a straight armor value to all troops. 10 makes sense to me, as even if you get hit by a bullet or piece of shrapnel, there is a fair chance it will it will just wing the soldier. However, except for the occasional flak vest, there is not real difference between a bullet hitting any solder from any nation involved in WW2.
Ranges in skirmish games can get kinda weird. If you try to come up with a consistent scale, any rifle or assault rifle can probably fire across the table. Even a pistol with a range of 100 yards can shoot a pretty good way on a larger scenario table.
Morale, combat values and special abilities are the key to differentiating the different armies.
German troops should have good morale.
Japanese troops would have good morale and infiltrate, but lower RC (supply was always an issue, and Japanese LMG and rifles were not the best quality).
Italian troops would have lower morale and lower RC.
US troops should have RC bumped to simulate superior supply.
British troops should have a straight baseline (I consider the brits to have good overall training, equipment and doctrine - so they get to be the baseline)
Russians should have lower morale and lower rc to reflect poor training and doctorine. They should also be cheap!
These values would need to be changed based on what period of the war the skirmish takes place in. For instance, early war Germans are very tough. The Poles, French, and Russians were simply not well trained for the new style of warfare, and should be penalized. However, during the late war, the German troops increasingly were less prepared, and supply issued began to reduce their combat value. US troops in '43 were not well prepared, and probably need a lower morale. However, as US troops began to get experience in '44 and '45, their combat values and good supply made them very effective.
Close Combat is another value that could be the same for all troops, but give a bonus to elites, jungle trained troops, or "desperation" situations (such as Russian troops in Stalingrad).
Squad specialists should be very limited in number. Light and Medium machine guns are freakin' deadly, and more than one per squad is going to make the scenario imbalanced. Snipers are individuals and not squad linked.
Hope those ideas give you some ideas to work with.
