Lowend makes some key points above, and to support his points, I just got back from the dyno testing/tuning one of my custom built carbs/spacers for a GM 350 crate 602 with the L31 Iron Vortec heads. This engine uses the same L31/heads as GM's 350 HO 330HP street crate engine. Weather they are Vortec 906 or 062, they work amazingly well, I did not go through the "Vortec head guide" as I base all my experience by what I work on, build and tune...so, direct feedback, like today. This engine is rated by GM @ 350 HP @ 5,400 and 396 TQ @ 3,800. It comes with 9.12 CR, Hyd FT cam with only .435/.460 lift with 212/222 @ .050 on a 112.5 LSA, all with stamped 1.5 rockers, we did not even take off the valve covers to adjust the valves, out of the "crate" , on the dyno, 2 quick FT/ring break in sessions for 20 minutes and let her fly..... Take a look at this dyno sheet, like Lowend states, making power with a basic 350 with Iron Vortec's is a walk in the park. No need for "high lift" cam, the Vortec head flows 230 CFM @ .435 lift, and a 350 cubic inch with that cfm will have a HP peak occurring around 5,400-5,500 rpm, just what GM states, and it hangs on not bad. The OEM's know more about CFM/runner shape/port speed/velocities/fill rate/VE/swirl/burn than most cheap over advertised/overseas copies, plus 100 other factors that most don't give the OEM's credit for. Now, if I was allowed to "modify" this engine, these heads could support 490hp, but that's a different story. And for my own shameless carb plug, note the AFR's and "fuel curves".....it's not much of a curve though.