You can eliminate everything except "stuff in the heater box." If t he car is running at normal temperature, and both hoses are HOT, then the problem is NOT coolant flow.
It's a blower/ air door problem
You have a shop manual, Matt? You talking about your 70?
There's a free 70 manual posted over at MyMopar. You have to play with the page numbers though, as they don't follow the "dash" Mopar numbering:
