Zircotec were sponsors of a race series I once took part in years ago and also noted their product was used on some GT40 replica's to good effect. No personal experience though. Camcoat was another exhaust coating used. But this won't work on a system that is wrapped prior (if I read the OP correctly). Issue with coating an exhaust in a white finish is that it shows every finger print afterwards. About as sensible as me wearing white jeans to work in my garage!
