holes in the dropouts mean it was originally sold as a timetrial frame. This came from the days when everything was drilled for timetrials - brake levers, gear leavers, brake calipers, even cranks.
the lack of braze ons was done (or not) cos it was thought 753 was too fragile to cope with extra brazing mid tube. In those days only a handful of builders could use 753 and I think it was raleigh who developed it with reynolds, so its poss that this was the only make of 753 in existence back then.
just editing to say there was also a silver one in addition to the three in the photo.
the lack of braze ons was done (or not) cos it was thought 753 was too fragile to cope with extra brazing mid tube. In those days only a handful of builders could use 753 and I think it was raleigh who developed it with reynolds, so its poss that this was the only make of 753 in existence back then.
just editing to say there was also a silver one in addition to the three in the photo.