My 72 Demon is a 3 bolt, I think it changed in 73. I bought a bunch of a/c parts from a guy who had a 72 Duster he was restoring. I had 3 a/c heater boxes date coded 72 at one time and all were 3 bolt motors. If you have a 4-bolt motor, don't think it's a 72 box.
I can get to the USPS tomorrow...