The best carb is one that is already tuned to your engine. An aftermarket carb (even though they say, "performs great right out of the box") is not tuned for a 351W. Its tuned to be a stabbing guess at something that will work on 100 different applications, so the chances that its right for your truck are slim.
Carbs are very complex mechanical pieces that perform a very simple function, but its important to note that if you carb is not working correctly its not because its no good, (requiring replacement) its because its worn out (needs to be rebuilt). The jetting and metering on that carb are correct for that engine, its just that the gaskets have cracked and the guts are full of dirt and junk. Otherwise its a chunk of aluminum and brass, so new parts will make it as good as new; of course providing its not cracked or something.
Try shopping around. A rebuild kit for that carb should be no more than $25 and it shouldn't take a mechanic more than an hour to rebuild it. The $400 number is pretty outrageous to me. I have a guy up the road that will rebuild mine for $50. I never asked how much it would be for them to put it on and tune it since I do that myself, but I can usually tune a carb in an hour or two tops.... and I'm not very good at it.
