There are two possiblities
1) make it historic than tech must be about ca 20 - 30% per stage + bonus for the east minors. I have no exact figures, but i know that only 30% of the german industry was "war industry" 1939 and the max output was 1944 under the full bombardment of the allied bombers, which could never really harm the military industial targetes, only the civil people. The gearms had enough manpower of the occoupied countries(KZ). The german economy was very effizent and manpower was never the problem, only oil was a nerve.
On the other side than 1945 when Japan surrenders and the full US power could go to Europa then they must be getting about ca 1000 mpps alone, whit 1000 of mustangs and P47 coming each month.
2)when you want it balanced then keep it as it is
bw