Trying to think back when I had the Mach1, IIRC correctly the deepend goes in the bottom. I could be wrong about that and I know someone will correct me. But on the other hand if I recall correctly from way back then (and you know my memory : the lights kept falling out on me... ::
Sorry John, I know I'm not much help here. It must be the beer talking.
The original sail panels have a circular metal collar around the opening which is flat over a short length of the collar which acts as a key for locating and retaining the light in the proper position with the deep edge at the bottom. My replacement sail panels didn't have the metal collar and I re-used them from the old panels.
Well John, it seems you've had your question answered already, but I thought I'd run up my thread count... If you think about the light being used to illuminate the area under it, the deep end would have to be down, to point the light down onto the interior. There, I did it, I got my one thread for the day.
Don't worry about it, Randy. Apparently there was a running change in '69. I just cut the new panel and it fits "good enough" for now, but I think I'll try to find a replacement for it eventually, as the curve in it near the quarter glass is also slightly different making it not fit quite as good as the other side.