Removing vent boxes

[bigeasy1]

I think you're right that they used several methods.My boxes in the pictures were also plastic,but they glassed completely over them.
I think that in the early seventies,a lot depended on who was doing the layup that particular day.I hate to say it,but the glass work in this boat,was very sloppy in the unseen areas like the bilge etc.
Several areas of way too much resin(puddles),and others of resin starved glass.I know it's not pleasant work,and they didn't have the working conditions of today.God only knows what these guys earned to do this dirty work. It's probably why there seems to be a big difference between some boats of the same year and models.