A couple quick notes.

Spray, the Blitz Black is a single stage top coat. If I read your comment correctly it implied that it was a primer. Which, BTW, you are 100% correct about, primer is not an ideal finish coat.

Andy, similar to ProZ's comment about the stripe taper. Probably the other two most famous cars with the wide stripes running the length of the car are the Cobra and the Shelby Mustangs (I assume these are your inspiration). Most folks don't realize it because of the optical nature of it, but the stripes on both those cars taper both at the front and the rear. It's slight, but it's there. There are a number of Cobra replica sites, probably ERA would be the best, and I think some Shelby GT sites, that have specs for stripe layout. You may want to track those down for a scalable example.