Auto body repair & detailing: 67 mustang rust work, radiator support, height measurements

Question
I'm restoring a "67 mustang coupe. Cant seem to get any straight answers and you came highly recommended. Rusted are both front frame rails, minor floor(to do a clean job will likely replace complete floor), and radiator support w/ lower cross brace. What would be the correct procedure in terms of what is changed first to keep all straight and squared. The frame rails are attached to the floor, do this first to keep correct height of rails when welded back in place, or rails first to lay floor down onto?  Any notes, "scary stuff", ect.  to be aware of during these replacements?  Thank you for any advice you can share.

Answer
Are you replacing the complete rail or just the floor support portion? Put the car on evenly placed jack stands under the rocker pinch welds and take height measurements to the garage floor. Use blocks of wood as to not crimp the pinch weld. Think of your car as a set of child's building blocks. Make sure everything is square and fits good before you weld anything. Use screws or bolts to attach the new parts first. It's a lot easier to remove a screw than cut a spot weld.