Fella's:
I posted a variation on this question in the Big Bolt section but you all seem to be close to my topic. I am just starting a '46 6400 project. The big truck has a second steel piece on each side, outside the chassis, to add strength. Over the years water and grit have worked their way into the crack. Based on people's enthusiasm for this POR 15 my initial thought was to scrape and vacuum this as good as possible and then force POR15 into it. This got me thinking about the compatibility of various Rust Convertors vs. clean, prime, paint systems, etching new metal, etc. Are there any compatibility issues to be aware of so that the final painting looks good and lasts long. Thanks!

Milk the cows you have