Once again, I had some choices to make. I had two heater boxes from 1970 and a nice clean one from 1973. The first thing I did was line everything up and closely examine the differences. For the most part, 1973 used many carry-over parts and part numbers. Since I'm not really a numbers guy, I looked at the parts for functionality. I started with the blower motor housing. For 1970 there is a timing sensor mounted in a hole in the front, that was eliminated in '73. I had a crack-free housing for '70, so I used that one.
The heater box had some changes, notably in the way the blend door linkage was configured. They appear to do the same function, so I went with the cleaner 1973 box.
1970 (notice the kick plate cover):
1973:
The lower vent cover was also changed in '73, from bolts to tension clips.
1970:
1973 (cover still attached):
The cores were the same as were the evaporator for the ac.
Everything was taken apart, scrubbed clean and set out to dry.
I purchased the heater box rebuild kit from DMT.
Mopar C Body 69-73 AC Heater Box Resto Rebuild Kit Set Fury Polara Newport DMT | eBay
I can't say enough about Detroit Muscle Technologies (DMT). I wish they could make all the parts I need, their attention to detail is extraordinary.
Laser cut and labeled:
One thing to note. When the instructions say to use 3m 77 spray adhesive and 3m black trim adhesive, don't go with the cheapo stuff. As stated earlier, you will end up doing the job twice!
Cheapo trim adhesive clogged and adhered to everything but the part: