I think your process with starting at the frame and suspension is the right one. Personally if you have the coin to spend, move onto the drivetrain and build the body around the engine/tranny already installed. If I had one torn apart like that I figure it's easier to install the body around the drivetrain than to install the drivetrain with the body installed.
Anybody who tackles trucks from the 30's and before has my respect as so much changed from one year to the next.
Good luck!
Jeff
