Floor Pan Replacement - GM A-body

[twertsy]

First, I'm by no means a pro. I purchased a very rough '70 GTO as my "guinea pig" project for a first time complete frame off resto. I'm touring the car so I'm not concerned with originality. It needs the entire floor pan, including trunk. My question deals with maintaining the integrity of the vehicle while doing this. They sell a complete floor pan (minus trunk) complete with crossmembers/floor supports. However, the car is on a rotisserie and I'm concerned with stressing the remainder of the vehicle. Do I need to do some bracing before cutting out the existing floor pan/braces? Should I take it off the rotisserie and perhaps do this while on the lift.....or body cart? Or, should I not purchase the complete floor pan and replace each section individually? To complicate it further, I'm also replacing the rockers.