Body/chassis first, unless you want to go in stages, or have plans for horsepower that can be handled by pretty much stock suspension. You can do a lot if you are planning on staying in the elevens and up. Example; hot small block, A body, get some good shocks, clam the rear springs as needed, slicks that can be run with the stock springs. Bigblock, same thing, just keep in mind that past about 11.0, it will get tough to get it hooked up.