First welcome to the site
I think your WAY ahead of yourself worrying about paint marks and the like at this point. Lots of work to do before that
We cant be sure of what the exact floor color would have been (should have looked and documented BEFORE you started blasting
So a guess based on other cars around your car, will be as close and you can get at this point unfortunately
For your plant and time period we would expect that from the firewall forward the frame rails, suspension points and front cross member would have been painted by hand with a red oxide epoxy primer sealer. From the firewall rearward with a batch color (a dark gray epoxy primer sealer with left over body color) that typically had some metallic in it and a slight blue tint.
The floor batch color would have stopped approx 3-4 inches before the rear cross member leaving those surfaces to rust quickly. Cross member was galvanized to reduce the rust.
Before any of this takes place on your car make sure that you construct some dolly tools and install them AFTER you have reproduced the galvanized surfaces of the floor rails.
Easiest way to communicate all the details is to send me an email directly and I'll send you a file and pictures...... too much writing to do it all again
There are rules though
but I'll explain