Nope, from my limited knowledge I am pretty sure that only Holley carbs have power valves, mostly all the rest use metering rods, and like Typhoon said they have springs in there that lift up the tapered rod to allow fuel in. Also, what kind of rpm are you running that 283 to, because that might even be a little more carb than you need? If it does lean out at higher rpms then its not such a big deal, but it could be that the metering rods and jets are sized for a bigger unit. Although carbs respond to air flow through them and only then do they add more fuel...if tuned right...it might be that at idle it is supplying too much fuel, which isn't a part of the main metering system in some cases. It is part of the idle circuit. So get those jets adjusted because the right jetting for your 283 with your 600cfm should also be the proper jetting for a 460. This may sound ludicrous, but the carb responds to more air, the more air it gets, the more fuel it adds. It's no doubt that the 460 will require more air, but the jetting will be the same, so get those figured out first. And check for vacuum leaks too. Hope this helps, good luck.