if those are your two choices of cams and youre set on that decision, then get the 2nd one...the first one is not even worth the money. i had the Crower 403 cams for the LS and it idled like 100% stock. as for your cat, the free method would be to gut it, but id suggest either a straight pipe or a high flow aftermarket cat. cam gears, dont get AEM, i had AEM and the bolts they use suck, they strip to easily...plus its only held on by 3 bolts...get something that has atleast 4. the retainers are a good idea since itll be much lighter than stock retainers, but they really arent "necessary", but it will be more efficient than the stock ones. same goes for the dual springs, you wont "need" them, but its a good idea to get it along with the cams. so, if you get the cams and the retainers and dual valve springs, youre probably going to want to raise your rev limit to about 7500-8000 at the most, in order to get the use out of those cams...but itll be worth the money in comparison to the first set of cams on stock valvetrain.