The heads I am talking about are a set of 450's and 416's. They are both 305 heads. I know the 450's were a earlier head but is there any physical diff. (flow capability) between the two?

 

The '450 castings are "Smog-Dog" heads, with likely smaller valves, certainly larger chambers (lower compression), and probably runner designs that go along with those drawbacks. If you can get the '416 castings instead, it's a definite improvement as a starting point.