I've thought about an updated version in SEA colors in place of the Invaders used in Vietnam.
If sufficently intact hulks would have been available in the Boneyard (but weren't in OTL), that would have actually made more sense: P-61 already had a radar (which could have been upgraded to one that could track ground targets) so would be inherently more suited to the night role.
Also, its turret was originally designed to fire sideways as an offensive weapon (instead of the Invader's two remote control defensive turrets), meaning that in a pinch it could have acted as a poor man's gunship, circling the area and strafing sideways (volume of fire and ammo capacity from four Ma Deuces on a nightfighter will obviously be lower than a cargo plane full of Miniguns and Vulcans). They even experimented with the turret automatically aiming and firing at targets designated by its radar already back in WW2, if the radar could have picked up trucks it should've made quite an impression on the Ho Chi Minh Trail (provided that the inability to aim downwards would not have prevented its use against ground targets).
I wonder if it had been called F/A-61K or AF-61K, or just F-61K?