Aircraft paint remover and a hand scraper, it took 2-3 layers of it some areas, lots of work and time but I thought it would be much easier than sandblasting as I really had a good solid body other than 3 floor sections, trunk floor section, quarter panels and the rear in between tail light section.
The underside I went at it with a wire wheel and sanding discs (80-120 grit). Cleaned it all off with reducer and POR15'd with a few brushes by hand.
The inside floor sections which were welded, around the front/rear windshield frames, and roofrails - used 80-100grit on the new sheet metal panels, and 100 grit on the rest of the good painted areas. POR15 painted only on the exposed metal/new sheet metal areas. Then I had sprayed POR15 self-etching primer onto those POR15'd sections so that when its all ready for paint/topcoat - it will adhere to that.
As for the underside, I bought the POR15 rubberized undercoating which will be sprayed on over the cured POR15 paint once I have the body all painted (will adhere to cured POR15 without sanding it,. and will cover any overspray that occurs in the meantime!) Don't see a necessity of UV resistant paint on the underside, unless you flip the car - it won't see the sun anyway, and either way if you didnt want to have rubber undercoating, you could always just spray a thin coat of their primer, then topcoat it whenever with any topcoat you'd like.
Great job, you are really doing a smashing job on your car. And yes the '68 body style does grow on you doesn't it.
Especially as you noticed after tearing it apart, it still shares most of the same underpinnings as the '65 model.
May I ask a few questions based on what I've seen from your pics?
1.) How did you strip all the paint off?
2.) What paint/coating did you use for the underside of the body? If it was POR15, did you use a UV resistant topcoat?