Highest flowing sbm heads?

Lots will dismiss this, but it's a good description of what it took to make 700+ hp from 440 inches of LS "small block"
The short list includes 14:1+, custom hydraulic lifters with only 0.012" of travel, 258/276 @.050 cam, and well over 8k rpm. Some things could probably be tweaked, but it gives some insight.

How to Upgrade a Stock Eliminator COPO Camaro LS7 Engine