They are out of a GT3 - DOT did not let Porsche bring the fixed back racing seat to the states in 2004. The stock 996 did not come with these seats either, but may have have had a similar sports seat option. These were pulled in order to installed Eurospec GT3 seats.
Here is a 2004 GT3 for sale w/ the same seats.
http://www.sportscarcompany.com/pors...T3_VIN2365.htm