I recall seeing some posts by MPandC, either here or on the Garage Journal forums where he had dealt with the windshield header rot. Looked like something I wouldn't want to tackle, but Robert is a professional. I think he could build a truck from scratch out of flat sheet metal.
Here's one guy's repair of a '59
Windshield header repairIf you go up to the top of the thread, you'll see some of Robert's advice. This isn't the one I was thinking of, but similar.