^true but I can't judge if those are actually the short GPMs or long(er) models from the pictures and can't zoom in close to enlarge that detail. Given the nutted brakes and other frame details I'd tend to think the DOs are from the earlier-than-late '70s gen and vote that this frame may be just on that cusp.
What size is the seatpost: 26.what? Can you get it sized at a shop with a "taper gauge" rather than vernier caliper?