One thing, with a Spit IX you don't have a material txt file yet, so you can't control the specularity, which for the SPit IX would be set non-glare, camo paint. SO I'm not sure anything you do will look quite right.
Kev had some really helpful ideas in one of the P-38 threads a while back. He divided a layer up into panel sections that ranged in shade from balck to almost white. Then he adjusted the opacity to make that layer just barely visible. Then he did a different layer, also based on panel sections, with each section shaded in a gradation from the edges inward. He overlayed these two layers and played with the opacity between them.
Pretty cool effect. Metal is tough - you gotta just keep playing with it. Somewhere I had a profile of a metal P-47. It was a jpg file and you can get colors for silver/aluminum from that....
Found it: