As the P-63 was not used in combat and it was just another version of the P-39, I agree the P-63 has no place.  But the P39 and the P61 do!  The P61 was not just a night fighter.  Yes, that is what they made it for, but I have found accounts of it being used for other things also.  Take away the night radar element of the plane and it is still a very powerful machine.  Strong airframe, big guns and engines that just wouldn't quit.  It flow like a fighter, could be used as a bomber.  It has a crew of three, but the top cannons could be operated by the pilot.  We have the Mosquito and it was less heavily armed than the P61.  The P-61 was in the same class as the Ki-45, Ju88-7b and the Mosquito NF.Mk II.  So, in short, the P-39 and the P-61 are planes which would be a welcome addition to compliment the planes we already have in place.