If everything goes according to plan (which probably won't happen), I am going to install SFCs and an 8 point roll bar in my 1970 Nova this winter. I understand diagonal measurements, but how do I check if the chassis is bowed up or sagging (vertically)? A local friend who has done it before says to put a big level (straightedge) up to the rocker to see if it's straight; is it really that simple?
If it isn't straight, how do I make it straight?

 

Certainly someone on here knows this kind of stuff.

 

So no one here has ever done this type of thing?