Brief Description: Drill seat back upper hinge F-637D
Cool thing here is that the hole spacing on this upper hinge is the same as the upper and lower horizontal angles. So, I just used one of the angles to match drill the upper hinge.
I made a modification in the location of the outside hole locations of this hinge. The plans show this hinge is to be shorter then the width of the seat back. And that the end holes are slightly interior from the rest of the holes that go through the vertical angles. Doing it this way will possibly compromise edge distance. Not that we need proper edge distance on a seat back but why compromise. I extended the hinge out to the edge of the set back and the end hole is the same distance from the edge as all the other holes in the vertical angle. I may shorten them up and round the ends off a bit.