I helped a friend in a similar situation with a '62 safari. He had no remaining floor in the rear half, very little perimeter floor in the front. If there are any precise measurements for the floor we couldn't find them.. Because the body floor fit is critical we decked the floor leaving at least 4" over size around the perimeter, [you can cut out for the front hold down plate]. Bolted deck to frame enough to get a precise fit, no bolts in outriggers yet. At this point you know originally the outside holes in the outriggers lined up with the bolt holes in the feet of your body bows. Bore out these holes in the plywood deck, set the body back down on the deck,[you may need thin shims under c-channel if outer skins hang down slightly], bolt it up. Check for fit, both measure and eyeball, triple check the door frame / door fit before you commit, now is the easy time to make slight adjustments here. When you're happy with it mark the entire outside parimeter. Remove the body, you're ready to cut. BUT you will have to determine the wee little bit INSIDE the line to cut to allow for a smooth exterior skin / belly pan seam. Not as difficult as it sounds and his came out perfect. That front right C-channel will be easy to make with the body in place, you can then make it to fit.