How to Check Uni body for Straightness

With what I'm seeing as far as corrosion, replacement rails and trans cross member would be in order. They are pretty far gone. By time you clean those up you'll come across much more perforation, damage, etc. Those forward most pieces that run from the inner rocker to the rail that have been cut need to be replaced. In essence it ties the rocker, floor, and rail together into the front torsion box area. pretty important for stiffness. Big block cars usually had an extra torsion box plate/reinforcement in this area. Height measurements are hard to establish without a level surface to establish points from such as a frame plate/jig or a frame machine and related measuring equipment. On a frame sheet everything is referenced from a datum line. All the length measurements are referenced along this horizontal line and the height measurements are referenced up or down from this line. You can take some quick comparative measurements with a tape and comparative side to side but those measurements you get will be off from a published frame sheet because you're measuring on different horizontal planes.You can drop plum bobs from frame holes, mark the floor, and take the lenghth , width , and x measurements that way for a little more accuracy. A rail being up or down might or might not change a length or width measurement which is why you really need 3D measuring. Always start under the "cabin" Square, length, width, and height, and then move towards the ends.