Headrest... OK, the full size drawings I have show the three views of the airframe in general arragement and place the end of the headrest at the first bulkhead behind the cockpit(not counting the bulkhead ending the cockpit). Not much till you consider the bulkheads are defined by the rivet/panel lines on the exterior. Makes sense structurely, the headrest can be supported by the bulkheads on both ends. What I don't have is the distance between bulkheads although I suppose it could be scaled from the drawing.