I used to own a '65, and can tell you that some parts are difficult to locate. You can find sheet metal though (used and some new). Bright work in good condition is hard to come by on the '65's. I would guess it's the same story on '66's. Whether to buy it depends on what you want to do with it and how much work you can do yourself. Early A's are probably the least desirable, so it's never gonna be worth much. I happen to be one of the few that like them. If you're going to hot rod it, headers are expensive (if they're still being made). If it's complete, and cheap, and you like it, and can do most of the work yourself, scoop it up.
