Does the body being bolted to the frame help you here in holding stuff in place or do you need to reinforce before cutting?
Probably. There is far less potential for distortion with things bolted together. But, it is going to get braced/pre-built just to be on the safe side before the plasma axe comes out to make all the space.
Today I emptied and dropped the gas tank (and filled Natasha's Camaro); got a fuel bath for my efforts. Sway bar, muffler, e-brake cables, shocks, etc are all out too. Just need to pull the differential and control arms once I am convinced I know what I am doing (LOL). Sized everything up and have a plan in my noodle on how to approach the build out of the new frame rails and how to reinforce all the effected areas. Including fully welding parts the factory glanced over.
Next step is degrime everything and get to welding.