it's fun, really
rule #1 there is no such thing as too many measurements.
rule #2 take pictures of EVERYTHING for reference. The things in the background are as important as the original object of the picture.
rule #3 unless you have a Boss 429 you can't afford to have someone else do it. Look at it as a challenge and a learning experience. You will learn how to weld, grind, paint, measure, cut off welds, re-weld, align panels, do internet research and by the time you are done you will have immense pride and satisfaction in a completing a project most people won't have the opportunity to do.
If you are doing this to make a buck, forget it. You have to want to do it.
I just finished my 69 Mach 1 with a Thoroughbred full floor. Absolutely useless customer support. I'm not surprised they are gone. I replaced almost every piece of sheet metal except the roof, cowl and door frames but then I've had the car since "81 so i'm attached to it. I have three years in this restoration and i just fired it up last week. I did a minor restoration on it in '85.
The bracing is helpful but more than likely your body is not square anyway so count on cutting the braces off when you put it together because the object is that it will be better than it is now. The braces are more useful to keep it from collapsing than alignment.This is a big project and if you're not a mechanical person it will be hard getting started but once you get into it, it will be progressively easier as you go. it's a lot of fun in a twisted way.
If it needs a floor pan, it's going to need a lot more as you open it up. And then you will want to add better suspension, play with the motor, maybe the trans, some cool guy interior, etc.
But first you need a place to work on it for awhile.
Take pictures and post a few.
Have fun and good luck!!