I feel like a butthole because heaters seem to start many threads...

You are looking in the AC section and not the heater? This manual, page 24-40 You got all the nuts going through the firewall?

[ame]http://www.abodyjoe.com/pictures/Misc.%20car%20info/70%20Dart%20Challenger%20Serv%20Man1.pdf[/ame]