late seventies heads vs j heads

[valiant360]

I got a pair of heads off a guy at work for free. 4027596 book says anywhere from 77-81 or something like that. Is there any real difference between say a pair of 70-71 j heads and these?

 

[AdamR]

No real difference.

 

[leblanc]

Just about the same, is what I was told too.

 

[moper]

The only one that jumps out at me is the AIR injection passages. Flow is down a little on the exh side because of that, but it's an easy fix to tap and plug the holes, and remove the bump in the port.