My '79 had water exactly as you described. So far, it seems my fix was as simple as some missing grommets on the firewall, main one being the one for the speedometer cable. I still see a little bit of water dripping down from driver's vent window in a heavy rain, as RWG75 mentions, but usually not even enough to reach the floor now. Mine would get wet all around dimmer switch and puddle all down the floor near exit/entry. Not any more. Before sealing the firewall I did pull cowl cover and get a vacuum and my hands in as much as I could to clean out any leaves, etc. but still had the leak. I check weather report whenever possible, and when heavy rains are forecasted, I have a HD tarp from Walmart, and I cover the cab, and use bungie cords to hold it down. Good for protecting it from rusting out.