You could use the same general rules for AA50, but you would have to pick one of the AA 50 setups (1941 or 1942) then add up the total cost of starting units to get the starting cash for each country. For one thing, I think there are less starting pieces for all the nations because AA 50 has a smaller map than the 1940 games so there are less pieces. Another thing is I think the prices are a little different in AA50 than in the 1940 games, plus you won’t have Tac Bombers or Mechanized Infantry as those units didn’t come out until the 1940 games.
Also, I’m not sure how you would handle China, since in AA50 they don’t actually get IPCs but rather 1 infantry for every 2 Chinese territories still under Chinese control at the beginning of their turn.
Other than a few small changes though, I think you could still adapt this idea to AA50.