On my 408 the best carb has been my 750hp. I tried a 950hp & a 830hp and neither one would out perform the 750. The 750hp was a factory carb I bought and set up and the other 2 were custom builds.Some people have good luck with custom built carbs but I haven't.

77 Aspen R/T 60'@1.41 10.76 @ 123.26

http://www.youtube.com/watch?v=Eya3Ue8KoZk