The water is most likley coming from the windshield seal, or a small rust hole in the cowl vents, had few that I caught in time before they got to bad, had the floor do that on my 76, ruined by a leaking windshield seal, I used mustang two floor pans, yes they do make patch panels , they were close enough to fix it, best after you remove all the seats and carpet hose down the car to find the leak or it will happen again,