Water coming from under dash

I have a 72 base Dart, 4 door, slant six, NO options. No PS, A/C, etc. Very stripped down model. I'm getting water in the car on driver and passenger side from under the dash in heavy prolonged downpours.

I'm going to try to seal the windshield first and see if that works. But I'm wondering if there are some common places of failure I can look at.

If it's coming un from the cowl, I have no idea how to get into that area. It looks all sealed to me from the engine compartment and the grill area under the windshield wipers. So how do I access that?

Any ideas, suggestions, help here would be MOST appreciated.

Mark