A few years ago I had posted some pictures of my bed assembly from Northern classic, 38-39's are the same as yours. If you do a search you should find that thread.
As I recall I had to fit the sub frame with the frame holes and then assembled the front and side panels. The fitting of my bed wood was next and with the S.S. divider strips that was probably the worst of it.
Also before I had the bed parts painted I fit and drilled out the fender mounting bolt holes. One of the first things I did do when I got my bed parts I had them cleaned and primed.
If you need I can dig out those instructions as they are probably close to what you have. Scott