Zach, that is probably an old truck heater from an early Dodge. Back in the 50's and 60's and even into the 70's a bit, it was generally an option to have a heater in a pickup or larger truck. Most were add-ons that bolted in like yours and had a manual door to allow heat to the floor. Some also had defrosters as well ducted from the top to the windshield. They were essentially just a heater core in a metal box with a fan on the back. Nothing fancy.
NAPA and JC Whitney and others also sold add-on heaters very similar. I've seen Modine and FoMoCo ones as well.
That's a pretty neat old piece and most likely just needs a heater core.
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