From Yaz' last game, 1983, via NESN:
If you're a cheap-seat regular like me, you know how much work this takes. This is the gap between the bleachers and the grandstand/RF boxes. These people would have had to meet up just behind the right field fence, each grabbed one side, and then each walked up--over seats, not on stairs--to their spot. Actually, they might have just wound up the sheet into a rope-shape and swung it across. But did the two holders even know each other? How would they have just happened to get seats right on the end and right even with each other? Or maybe it started at the bottom and people just kept passing it up to get it to the desired height.

Also note, if you've only been to Fenway in the past decade or so, the bleachers used to be cut off from the rest of the park. In fact, that's my favorite "Fenway improvement," but nobody ever talks about it. So this maneuver would have been even harder to plan back in 1983, assuming the two people knew each other, as they wouldn't have even entered the same gate. Anyway, in that same shot today, in the background inside the gap, you'd see fans walking around and food stands and that wide staircase, but in that pic you see a bunch of nothing, as it was just "the laundry" back there, in an area where fans weren't allowed.