Just a tip. I bought a brand new 87 442 once and had a heckuva time getting a leak fixed that looks eerily similar to your floorpan. Turned out there was a weld section on the cowl that had an air pocket apparently in the seam sealer applied at the plant. Left a small entry point for water to drain in when it rained or you washed the car. It ran down the front by the emerg. brake pedal, found a trough, and settled in the rear floorboard. The front carpet felt dry. They changed T-top seals twice and could never find it. I finally got fed up and took out the carpet one day and had the wife spray the pee out of it all over the car and finally found it. Wasn't easy to reach with the fenders on, but if you remove the fenders, check out all your seam sealer.