I would not recommend using POR15 for concours restoration. The rust preventive coating is very glossy, thick, and hard to paint over if cured. It is also not UV resistant. The rust preventive coating does not stick well to clean bare steel and if you take a pressure washer to a panel which didn't have a rough surface when it was applied the POR15 will come off in sheets. I used a garden hose on a clean steel toeboard I had painted with POR15 and it lifted off in sheets. The product adheres well to rusty surfaces.
If you want to paint over POR15 you could use their Tie coat before it cures or spray a light dusting of primer before it cures.
For daily drivers it may be okay but I've used Masters series silver and their chassis black top coat and find them easier to use. MS silver is UV resistant and paintable when cured.
My humble observation.