I think correcting the P-47s shouldn't be too much of a problem
As for the belting. That is, I think anyways, a more complex issue. As it stands right now there is one piece of code for all M2 .50cals (to the best of my knowledge anyways). So if you change the belting on one... you change it on all. Really the API/APIT late war ammo should probably only show up on a couple of aircraft. Say the P-38L Late, P-47D, maybe the D-27 and the P-51D-20. Not sure if that type of ammo saw usage in the Pacific either... I don't know.
So how do you get the loadout right? Optional ammo belting built in to the game? If so then it's a bigger task to get that right for every aircraft type and for every gun too. I think that'd be incredibly cool but a large task for sure.