Hi guys, I need to order a new radiator cap for my '69 Mach 1. It's a 351W car, built June 5th at Metuchen. I noticed NPD offers two versions of the cap, both labeled as concours correct. One is zinc/Autolite (8100-2A), and the other is satin chrome/Autolite (8100-2B). Which is correct for my application?