Head casting number = ??????

[DeWynter]

I have a set of heads from a 1970 corvette. The casting number is 458642.
other numbers on the head are J 30 6. I have searched for over an hour to find the specs on this head but to no avail. I need to know thw chamber size and valve size, as I want to know if I should use these heads or try to get a good set of 350 centerbolts. I really dont need the 2.02/1.60 valves as a set of 1.945/1.505 are good for my application, I need the velocity not the flow.
I have a small stress crack in the other set of heads I have, and have this other set of heads just lyin about, they are polished and port matched to the gaskets for a TPI. Im just worried about compression as these are from a 70 corvette they may have 60cc chambers.

[DeWynter]

is there a way to decode this number? does the code break down into smaller codes eg. 458642= 45 86 42 or 458 642. I can find lots of places where this head is mentioned but never the specs just year and engine size.

[Joe 1320]

I'll search for my interchange manual and decode it. Ya just have to wait till later tonight.