When we changed the heater core on our '66 Newport 383 factory a/c car, back in about 1975 or so, the orig Chrysler part number had changed a few times at that time, BUT a final supercession part number was found. So it was ordered and installed. When I later asked the parts guy what the part number fit, he looked through several Chrysler parts books, price schedules, and finally came up with "1970 Charger w/factory air". I thought that was interesting and thanked him for his time. BTW, the new heater core worked just as good as the original one did.
Reason for the replacement? Typical fogging of the windshield on Defrost mode and wet carpet on the rh front footwell.
Just some recollections,
CBODY67