Karnak: The Spit5 was reverted back to normal. Don't forget it started the way it is now, only with 2x the cannon ammo. They just restored it.
As for the P-38G, I don't think you're right. I recall 2 P-38 models going way way way back. One was the G and the other I thought the L. When we had the 38s remodeled/updated they added the J. I recall all the fuss on the forums, people kept calling it the PJ etc. Now I could be getting the J and L mixed up because they are so similar, however I'm pretty sure the G was around for a long time before that.
P.S. I did include the Ki-84... Look at the bottom of my list

Iwo: The 40mm was such a terrible weapon with such bad speed and trajectory and reliability that you had to fire it nearly point blank, in which case it wasn't doing you any good. That's why they went to the 20mm loadout after the abyssmal (yes, abyssmal) performance of the 40mm. The Japanese 40mm and 30mm guns were really not desirable weapons.