1968 '340' Barracuda vs 1968 '383' Road Runner

Not talking about the gear, that's common knowledge. what is this package, carb, intake, and cam. Do you have some documentation that showed a package with a P mopar number from dealers? Or is this just something the parts counter guy would special order not having much to do with the dealer, I don't see dealers back then stocking 750's, aluminum intakes, and cams to install.