here is some information from the harrison book concerning Italy and here economic capabilities in 1942.
Here’s another roughly accurate source of of GDP listings through-out the ages.
I’ve redone all the IPC values for my games awhile ago. I assigned a value to every territory on the board including neutrals, except for the Sahara and some of the itty-bitty pacific islands.
After several revisions, I’ve settled with the following numbers…
USSR 47 (before germany invaded)
Germany (and nations under its influence) 119
British Empire 92 (India alone is 22)
Japanese Empire 55
USA (states only + panama) 172
China 24 (split between US and Japan)
South America 25
Russia simply has no chance and is always crushed by Germany if you use the revised or classic maps original unit setups.
The game does get fun and out of hand very quickly dealing with tons of IPCs and huge masses of units.
Email me at firstname.lastname@example.org if you want a copy of a map with these different IPC values and how I figured them out.