Cam & engine gurus gtf in her meow!

Headers work in a couple of ways.
Firstly;
they create a lo-pressure pocket behind the exhaust valve, so that when it opens, the exhaust is desperate to leave the cylinder. This frees up some power that would have otherwise been used to push that exhaust out.
Secondly;
If your cam has significant overlap, such that both valves are open simultaneously at the changeover from exhaust stroke to intake stroke, the low-pressure in the primary pipes, will help the atmosphere push AF charge into the cylinder, before the piston is actually officially moving down on the intake stroke.
But this phenomenon does not happen until the rpm is up hi enough to get it started, usually in the early to mid 2000 rpms.
And it is most effective at some higher rpm to which the cam is tuned for, and over a fairly narrow rpm band say 1500 rpm or less.

So the gist of this points to headers working best from the torque peak to the power peak and beyond. How do you get there with 3.21s and I'll assume 28" tall tires?
Answer; slowly.
and with a bigger cam and still a nominal 8/1 compression ratio; probably slower than stock.