http://www.hinsonsupercars.com/
These are cool cars. The LSx conversion adds very little weight to the car, actually Hinson's says that they may be a little lighter with the V8 in place of the rotary with the sequential turbos.
I seroiusly considered doing one of these a few months back when I had a line on a 95 RX7 with a bad engine. Body was too rough and I didn't end up buying it.