Just a thought but I installed tubular headers on my '70 GS455 clone in '92 and I drove the car daily three seasons a year until 2006. The headers never rusted out; definitely not 300 SS. Every couple years I painted them with Eastwood Tool Co's exhaust manifold paint. I just wired brushed them, and painted with a brush; they looked new for another two years. But those tubes get really hot and baked that paint in. Not the best pic but you get the idea. Maybe you can give Eastwood a call and see what they can do for you re: high temp exhaust paint, to fight that rust
