I bought full length floor pans for my 67 Coupe.  (The 50" long Pieces) I want to change them myself, if I cut out on side along the tunnel, as described in the procedure, will the car collapse??? Will doing one side at a time leave sufficient strength to keep the unibody from bending? The car is fully assembled now, less engine. The floor pans aren't in bad shape, they just have some rot through in a couple of places, the only reason we're changing them is to avoid doing it later. Thanks in advance.  

I wish I took pics of my 68 hack out. I had solid rockers and torque boxes, I tore out drivers and pass. side floors plus the rears. I bought new seat risers too. My answer is as long as the inner /outer rockers are good you can rip all the flooring out. The floors are only somewhat structural. I used a air powered cut off wheel a air hammer, spot weld cutter, nice chisel and a mig. welder plus my favorite 5lb. hammer. -Ron  

Do one side at a time.  Keep the opposite door shut all the time. Example: if you are replacing the driver's side leave the passenger door closed. Lean in but don't climb into the car when cutting or welding the floor.  You should be fine.
ED