I found a near perfect original paint longbed from out west and cut it down. Don't be upset long bed guys, I paid a lot of $ for it
The cutting and putting it back together part are easy... fully welding it and having the bedside look like this when you're done is no easy task.
The last pic is the Z cut template. When you put a straight edge on the back of the bed, you'll clearly see where the bed "falls off and curves" to the taillights. That's your first line, basically the back edge of the turn signal, 8" over is your 2nd line. My truck is a 67 so I just cut out the turn signal.
I did have an original short bed I kept taking measurements from too.