Well that little can of Silver seal appears to have stopped the leak in heater core. Just as Nate suggested, I ran the truck for a good 30 minutes and the floor and windshield bone dry! Thanks Nate for sharing your wisdom!!!
Silver Seal You're welcome . Often the simplest ways are also the best . FWIW , the BIG THREE American car makers have been using this in the initial assembly for decades , it's that good .
What radiator cap you got on it? If you have much pressure at all, these old systems will find the weakest point and leak. I've read they were designed to run no-pressure, and we used to run 'em with radiator caps half-on (loose but on) and they'd never barf, even overloaded with grain on the trip to town. I'm hearing a 4# cap is about as high a pressure as you wanna put on them.