428 used high compression D 72cc like 16 and 48, the heads on the 455HO are 111cc and it seems maybe they used the 1.5 geometry in the rocker area instead of the RAIV 1.65. Many people have proven the D ports can be made to flow as well as the round ports, and you would probably tell little difference at the track. I will go performance over the stigma of some hard to find heads until such time my pocket book is endless.
In contrast a few lucky people have the rarest exotic Pontiac goodies, for example Tom (TJS). A very nice person who has some of the hardest to find factory stuff, and has the means to use it well. I admire that, but he is in different league than me at this time.
So I go for the quickest my buck can buy, I won't waste time chasing 111cc round ports. There is nothing wrong with it, if that's what a person needs.The may actually be a good head to use with a blower set up.
There is just too much horsepower loss by running 111cc on a flat top with 8.1 compression, compared to the same motor with some 72cc would make 11.0. I have heard it estimated that each compression point is worth about 50 HP.
