We just replaced the wood floor in the back of a 64 panel for a customer and the pics can be found
here. Before the comments start...Yes I know it has that "USLESS" giant chassis stepnotch and full width wheel tub and notch cover on a truck with airride. The same process that we used to convert what was left of this floor area can be used to support and create a new FULL floor on any wood floored panel/burban. We used 3/4 square tubing and made a perimeter frame that was welded onto the sheetmetal interior panels and tied to the bodymounts/floorbraces. This was skinned with 16 gauge steel and plugwelded to the 3/4 tubing and front/rear floor sills (where the recess is for the original plywood floor). From my experience installing the floor in several pieces is the best way to go because of the angles of the bodysides. (it's widest at the bottom where the floor is installed) If you think this may be something you want to tackle take a look at the pics and even give me a call at the shop if you want.
JOHN@ CCC
314-968-8377