Wow! That's nice. Most people wouldn't want their car seen that naked. Me included. Oh you could get there with some 80 grit and a lot of time.
Hey, In this day and age, anyone who shoots real automotive finish over an old paint finish is a fool!, there, I said it! To get a metal body to the stage of the Merc in the spraybooth would take several steps. I'd start with removal of all the trim & gl***. Next a heavy coat of "aircraft grade" paint stripper. Don't waste you time or money on "hardware-store" grade stripper! Several coats of old paint can be stripped if you use the stripper in 65-70 degree weather or better. Cold weather and stripper don't work well together. When you hit old repaired areas, plan on the removal of all old filler, given you don't know what's under them. Once the last layer of stripped paint is removed, sand the panel, one by one with 80 grit, followed up by 150 grit. Use a Da, jitter bug, idiot stick or a sanding block, but sand all the panels until no old paint can be found on the surface of the steel. Some would follow this up with 220 grit, but I like to leave the metal with alittle "tooth" for the primer to grab to. At the very least, a wash with some sort of phosforic acid, followed by a lacquer thinner wash and an etching primer would be a good start. Be sure the primer you choose to spray over the etching primer is compatable with etch primer, some arn't! Some like plastic filler over the etch or epoxy primer, I don't, but the filler must be covered with a primer prior to a sealer coat, on you way to a top coat. S****ey Devils C.C. " Spending a nation into generational debt is not an act of comp***ion !"