I will second, or third, the fact that stock injectors are really hard to get out. The passenger side ones were not going to come out at all. Finally, when they did the little hats pulled off the injectors and the o rings stayed behind as well. No big deal unless you were planning to re-use the injectors. I pried carefully up on each injector individually.
Make sure the O-ring bores in both the fuel rail and the manifold are really clean and smooth. I used a stiff plastic rod to push a solvent soaked rag into each bore to clean them, Do not scratch them or you will have a vacuum leak into the manifold and/or a fuel leak on the fuel rail end. Use motor oil to lube the new O-rings. I bought a bag of 16 O-rings from GM, meant for a V8 but its nice to have spares. The new ones use a harder blue rubber.
I assembled the new injectors into the rail on the bench and plugged them all in before putting them back on the car, makes it easier to connect them all right.