Going by the 1958-59 Chevies (and other GM cars, which mostly used the same white, except perhaps Cadillac), the white should be ever so slightly off-white, and may look more cream/ivory in color before drying.
Scale Finishes and MCW use their respective paint manufacturer's mixing formulae (Dave at MCW uses PPG lacquer, Scale Finishes uses whoever makes their paint, I believe Jameson uses Sherwin-Williams, but I'm not sure). While the codes and final results might vary slightly, all the samples, regardless of paint type or manufacturer, should be probably within about a shade of each other.
Charlie Larkin