A bit on the never much liked P-39 and -40.
The P-39 will not receive that heavy and numerous armament set-up - kills the rate of climb and speed instead Axis machines & men. At the end of the day, it would be probably a belt-fed 20mm through the prop and two .50s. Not over-doing radio sets and armour suite would also keep the weight acceptable. Once the better V-1710s are available (hopefully a bit before mid-1942 as historically) adding a bit of fuel, both internal and external should be done.
The P-40 - no more than 4 .50s. Burrying two coolers in the wing, as done with the XP-40Q might shave some drag. Try and fit 150 gal drop tank under the centreline ASAP.
Once the firing starts, the USAAF will get some British-produced aircraft, as in OTL. Like the Spitfire V - see whether the 150 gal DT can fit, install the 30-35 gal tank behind the pilot (similar to what was done historically). Perhaps some Bendix carbs can be retro-fitted (gain 10 mph vs. float-type), also a bit better stacks (gains 7-8 mph). Perhaps delete four .303s and install two .50s per aircraft.
Once Spitfire VII/VIII/XI is available, try to shove as much of fuel on these as possible. Get as much of Mosquitoes as possible.
The P-39 will not receive that heavy and numerous armament set-up - kills the rate of climb and speed instead Axis machines & men. At the end of the day, it would be probably a belt-fed 20mm through the prop and two .50s. Not over-doing radio sets and armour suite would also keep the weight acceptable. Once the better V-1710s are available (hopefully a bit before mid-1942 as historically) adding a bit of fuel, both internal and external should be done.
The P-40 - no more than 4 .50s. Burrying two coolers in the wing, as done with the XP-40Q might shave some drag. Try and fit 150 gal drop tank under the centreline ASAP.
Once the firing starts, the USAAF will get some British-produced aircraft, as in OTL. Like the Spitfire V - see whether the 150 gal DT can fit, install the 30-35 gal tank behind the pilot (similar to what was done historically). Perhaps some Bendix carbs can be retro-fitted (gain 10 mph vs. float-type), also a bit better stacks (gains 7-8 mph). Perhaps delete four .303s and install two .50s per aircraft.
Once Spitfire VII/VIII/XI is available, try to shove as much of fuel on these as possible. Get as much of Mosquitoes as possible.