I have a 1969 GTX factory AC car in my shop. The owner had it rebuilt a few years ago. The AC box. they put a plastic drip pan in it under the evaporator, they were steel from the factory. I have a mint factory steel drip pan. I took the box apart and the evaporator has 2 of the 4 mounting points are wrong. I can make it work with some fab work I think, but the owner is wondering how many different evaporators and drip pans there are in 1969. I think this is a after market evaporator and its meant for the plastic drip pan and not the steel. anyone know the story on AC evaporators and drip pans

I've rebuilt AC boxes in 69 Charger and 70 Road Runner. The drain pans were always metal, and the numerous donors I took apart in boneyards were the same. In addition, I managed to dig up a NOS drain pan many years ago and it was identical to the OE piece. I agree with your hypothesis, the 'rebuilt a few years ago' replaced the evaporator with an aftermarket including a matched, plastic drain pan.