Man that is a crazy amount of work.
I admire your ambition.
Looking really good.
There is a product called Ospho that you might want to investigate. I have tried it on rusted steel and I am very impressed with it.
All you are trying to do is prepare the surface for painting so that the paint will durably bond to the metal.
Bob near Winnipeg
1986 F250 Lariat extended cab 300 T18 2WD
1979 Honda CX500
1992 Oldsmobile 98 touring sedan
2007 F250 6.0 4wd