I got an assembly manual for my 1964 Fleetside and I have only used it for finding out where the spot welds are on the rockers.
It seems to have a lot of useful info but if the guys assembling those things had only this book I have to look at they had a pretty good idea of how the trucks went together. I also had to study mine quite a bit because it seems as though there were no thought or organization of how the different pages went in. It looks like they just sort of threw them in.