i did alot of reading on manifold heat before i did my super six conversion, what i came up with was this: for a street driven, carburated, vehicle, manifold heat is prefered.:read2: the "hot spot" helps fuel atomization. it also gives you a more consistant manifold temp to tune to. these are less of a factor when running at high revs (racing) as the air velocity is high enough to atomize the fuel.
here is what i made for mine from 1/2" plate.