How to make sure your car is level ?

Is there a fool proof way to make sure my cuda is level for torque boxes and subframe connectors when it is just a shell? No torsion bars or shocks and all the bushings need to be replaced. Can i do this or is it better to replace everything first? I've seen where they weld bars across the inside of the shell on convertibles also would that be a good idea? I would like to do this on a rotisserie but i dont want to mess it up thanks?
Author: Cudachuck