I am currently in the home stretch of doing all these repairs on my '71 long. I did not worry about removing any paint because I could see where it was rusting. I immediately started right in at removing the rusty rockers, inner rockers, hinge pillars and kick panels.
I removed the entire inner and outer rockers because they were completely gone. For the other areas I just removed as much material as necessary to get solid metal. So, A-pillar bottoms, kick panel bottoms, floor next to kick panel. And a few patches in the floor next to inner rockers as necessary. Oh, and B-pillar bottoms. Cab corners I patched up with homemade patches. I also made the kick panel bottoms by using cut out metal as a template/guide.
Then I sanded back the paint to a feather edge near the repairs, primed (x2), sealed, finish coat
Did the same to the door bottoms. Also, if superficial rust existed where I did not cut out metal, I used a phosphoric acid water mixture to neutralize the rust (then topcoated).
In the image you can see that I epoxy primed the cab floor (which I did not replace)...I simply used a scouring pad on my angle grinder to get rid of glue and other junk. Then I primed.
Currently prepping fenders (wings for those across the pond) for paint. Doors and cab interior are 100% done. FYI, I used Precision press on door seals and they are perfect and I do not have to slam the doors. I was careful to ensure the door was positioned in the door jamb uniformly before calling it good. This ensured the door seal was compressed even all around for good shutting doors.
Good luck.
