I'm gonna take a crack at this one .
Tuned headers are a certain diameter and a certain length....for a certain RPM for a certain sized engine. Clear wink .
Timed headers are the 180 deg type.
The (oldschool) chev firing order is 18436572.
The header for one side would be 1467
The header for the other would be 8352
This would lead to a exhaust pulse reaching the collector at a certain time to help either scavenge the cylinder better and to (or not to) affect the next cylinder in line to fire an exhaust pulse.
I'm not really sure about the cam profile part but I would listen to the theories that would come of this discussion