(Hit the wrong key and sent the post before completing my comments...) We installed the front doors in order to begin to determine the placement of the rear section by inserting the center posts and then strapping the front doors, center posts, and rear doors together to begin to get a rough estimate of the rear tub. We also removed the braces that were rivited to the body so that we could string a wire across these dimensions to pull the body flex up tight. Its amazing how much sag and flex there is inthe sheet metal before the wood is attached. As a side note, we used sheetrock screwws or something similar to set general placement, and then removed them or depending on the joint, ran them up tight for the final fit. Once the floor section is determined to be correct, we moved to the body wood and finally the top. We also completely fitted all of the wood before tearing everything down and coming back up with final gluing and screwing. The process is not difficult, just very time consuming and will require several test fits before the final gaps can be determined for doors and final alignment of panels. One area that we did go back and "re-do" once the final fit had been completed, was to disassemble the center posts assemblies and take an additional quarter-inch off the sides of the wood post. This allowed for more clearance between the doors and the post(s). I may have some patterns for floor sills etc. if you need, but regardless, please let me know if I can give you any guidance (based on my experieces) as you progress through this phase of your restoration.
Good Luck --
Dick