I would just about bet your cab under the upper windshield gasket on the driver side is bad too. A person handy with a mig welder could weld in good metal to replace the holy metal. Metal donated from another 70's ford cab in the same area would work best, because the natural contour/bend of it would fit yours. That would be a lot easier than replacing a whole roof. If is so badly rusted that the roof needs replaced, I would think the cab corners are probaly rusty too, and then a total cab replacement might just be easier than all the patching. good luck to you, all jmo