A body shop owner north of Nashville who specializes in restoring old Mustangs built a jig to position the body while he changes the floor pans. He stays booked ahead about 18 months because his work is so accurate. We had a similar jig for checking the frame on our round track cars during wreck repairs. Without a solid fixture to work with, it's almost impossible to get a good installation on a floor pan or other major sheet metal part.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!