I have an 89 SHO winter car. I had the same problem as you, the car runs great and everything works, but the body was terrible. I had holes in the middle of my doors! I fixed mine 3 years ago. Here is my advice. Go to UAP and get their body metal (about $25.00 for 3 foot by 6 foot), this stuff never rusts, even where you cut it. It must have some kind of alloy in it. Make paper templates of everything you need (you can buy outer rocker panels, but that is it). Transfer it onto your metal, and use a jig saw with a metal blade to cut it out (you don't have a wavy line at the edge). Be prepared to make lots of small pieces like the lip over your wheel welds, I bent my 1" edges on a workmate clamped tight. Try to make a tab on your last panel that can be picked up by a tab on your next panel. I painted both sides of this metal and installed it with pop rivets, shape it as best you can before you put it on. You will be surprised how well it turns out with no bodyfill or anything to smooth it out. I put on some body fill to hide the places where the new metal joined the old car and just scraped it flush. Add fill to corners like the wheel well lip and scrape it flush. If you have any ability, you can body fill the whole panel and shape and sand the surface, but I found I had no ability to do this and it was actually better to leave it alone. At this point you can take it to someone who can do it, or you can spray bomb it, like I did. It has been 3 years and none of the panels has lifted or misbehaved and it still looks presentable. I did not cut out any old metal, just clean it up and prepaint it with tremclad rust paint or whatever. This may not get you any show awards, but I am still surprised at how long it has lasted and how good it looks for the effort by someone with absolutely no skill in bodywork. My car was black, so matching paint was not a big issue, so you may have some extra work there.