I think it was mid-way through 05, as I've seen mention that some 05's got them and some didn't. Using up leftover stock I guess. You would be best served to change the LIM gaskets anyway while the motor is out, along w/ the valve cover gaskets and grommets. You will also need injector o-rings for this since you have to remove them to get to the LIM.
BTW, didn't the 03 GTP come w/ the Gen 3 already on it???