I doubt that the GPM version of "shorty" dropouts were on the scene much earlier (and probably later) than the Campys, and genrerally those were considered to be "introduced" in '78...some big hitters may have been able to get some a year or so earlier. I bet it's no earlier than '77, very possible a tiny bit later, but...what rear spacing: 120 or 126?
Great color, BTW!