There really isn't any "correct" shade of red-oxide primer. Ford probably used 100 different variants for 64.5-73, not to mention other colors. We normally recommend that areas of a car be cleaned and primers color-matched for the most authentic restoration. It wouldn't be unusual to find several color or shades of primers used throughout one car.
For those that just want a generic, cookie-cutter type of primer, most use something like PPG DP74LF. They may tint it slightly, but it's usually decent out of the can.