Darren,
Frequently, projects tend to change and evolve as we work on them; they sometimes take on a life of their own. I would say that this truck of yours fits into that category. So when it comes time to decide on how to paint it, let it speak to you as it has all along. Rusty and crusty or shiny and sparkly, do what's right for the build. Don't ever limit yourself! ...though I don't think you really have a problem in that area...
Regards,
David G.