Unless I'm missing something this is fairly major surgery. I know I'm stating the obvious but presumably you have a frame jig lined up for this job. Not much is going to be left of the OE unibody as you're pretty close to full tube chassis territory. At the same time most people in this situation don't make these kind of 'retro' aesthetic choices and the body ends up very low with 14x32" tires tucked under the wheel openings. Never liked the way those types of cars look myself but I get they are purpose built and a period correct appearance is likely low on the priority list.
I know you've studied this stuff to a finite degree but that said - how was this sort of thing done in 1971 (if it was) and are you going about it in a different way? Did individual racers make their own choices or were there directives given out from engineering? The Missile was the model but it's hard to know how much of that data was given out to the privateers.
What is the floor going to be like when finished, just panels? Imagine the trans tunnel will be removable for service.
Good luck with this.