There's a big motor behind that firewall and it will heat up everything around it. Same for the "hump", due to exhaust. When I rebuilt my car I put a lot of insulating material in these areas and it helped immensely.
Also the HVAC systems in these old cars don't dehumidify as effectively as in modern cars. Modern cars use a combination of the AC circuit and the heat circuit to dehumidify. Before I modified mine with a Vintage Air Gen IV system I had to have a towel handy to defrost the windshield.