With the '76 heads, eventhough flow might be better, you still throw away a half point of compression ratio, piston-quench is def. out the window aswell, and if the heads were rebuild and had a valve job, the grinder most likely ground through the hardened area of the seats, leaving you with unhardened seats again.
I would stick with the stock heads and it's 4-bolt valvecovers, or better spend the money on a much more torqier 413 orso.
