Rick,
When I get back to my home computer I need to send you some pics of my cowl. My car was/is a non-air model. There are two large oval vents that go on either side of the cowl just in front of the hinge pillar. They have a rubber gasket that has to close off an otherwise large gap between the cowl vent opening and the vent flap. If yours is like mine was, that rubber is long gone and you have a constant source of engine heat rolling into the car.
This should be fresh cowl air from under the windshield. However, here in Florida the engine heat seems to over power it. Plus, the outside air temp is hot to begin with. So, you are ramming hot atmosphere air in with a supercharge of engine heat from the firewall right onto your toes.
Plus, there are two ports just above the main vents that are open all the time. They are each about 2" in diameter. That means you have another 4" of hot air getting under the dash.
With a non-air car, I don't know the solution. Since I am running a vintage air under the dash unit, I sealed these off for good.
BTW-Prior to deciding on the vintage air system, I was able to pick up the entire factory a/c system including a near perfect control panel, vacuum lines, in dash and firewall side ducts, housing, evaporator, heater core, and blower motor. The only thing I don't have would be the condensor, lines, and compressor. I was planning on making fresh R-134 compatible lines and running a late model R-4 style compressor.
I think I will be trying to sell what I have soon. Not sure what it is all worth-but thinking about asking $400. What do you think?
Chris