A problem solved? Air comes into the cab through a 10" X 2" vent in the cowl just under the front windshield. It can be turned on and off, but over the decades the insulation seal is not doing as it should. Because of the location of the AC blower in the trunk it is very difficult to access. I have been trying to come up with a way to block it off from the outside. Here is my solution using super strong magnets and a rubber matt material that will not damage the paint. I took her out for a spin and it worked. I'd say 99% of the air flow is gone. Just call me Macgyver.
Retired and enjoying doing squat.