You are right in the ball park for shift points and RPMs for that size motor. I shift at 7000-7200 and trap at 7500 with a 446 ( shows no signs of laying over)
more compression would help, but I dont recommed it if you will street it a lot. I would definately go with Harland sharp 1.6s, could net you around 25-30 HP
have you experimented with valve lash changes?
what carb? What manifold?
spacers?
2" is the right header, but I would imagine it is a bit too long being fenderwells. would want 32-33" long with 3.5 collector around 16-18 "

YOU are pretty close to maxed out there, but there is ALWAYS more to be found.
look at the suggestions and see what you could do.