Full floor pan install

I agree with not overthinking it to a point. It's not going to fold up, however here is that point. Concrete floors arent dead level. I had to shim 2 of my stands to get the empty car body dead level. If its not level when you install the pan, the induced twist in it will remain after its welded up. I have seen and fixed twist on full frame car chassis from people jacking up one side, and welding in bracing for a frame hitch. Then down jack the ***** and wonder why it drives crooked. I personally sawed out a C channel from a full framed GM car then had to un shim the upper control arms because they gave it a twist when they welded the C channel in then shimmed the living hell out of one side to make it drive straight.

These cars "WERE" assembled on level and square jigs on the assembly line. This kept the chassis square until everything that was going to be welded on, was welded on.

Dont believe me? Pop the plastic plugs in the trunk floor and transition pan that line up over the framerails and look straight down through them. The framerails have corresponding same sized holes in these locations. I'd venture a bet that these frame jigs had very specific diameter pins with a shoulders machined into each of them. The front and rear rails were set into them. The pans and pieces were set on the same pins to line them up, clamped down and welded. These jigs were also set up to build both the barracuda/duster 108" wheelbase chassis and the dart/scamp chassis which was I think 111". Yep the holes were left on the framerail side as drains, but that was not their initial purpose.