The big issue with the RX7 V8 swap, IMO is the insufficient space for tires. Apparently one guy has managed to get a 275/16 in his stock rear wheel well, but I'm not sure what he had to do to get that in there. I'd advise a good widebody kit, since it'll drop some weight too.
These are just bolt on flares, the cheapest and easiest way to go.
These are some very high quality race bodies, and are signifigantly lighter than the stock sheet metal. I'm probably going to go with the GT3 kit, when I get to that point.
http://www.mariahmotorsports.com/ext...ngbodypkgs.htm