Let's take the header debate a step farther, with the cam, head and intake he has header choice is not going to add much, just stick with the 1 5/8" shorties you got, you may gain a few hp points with long tubes,like maybe 10hp, but the biggest gain, although still small, will be the low end torque points, and going to a bigger tube size likely will kill torque more without adding hp.
All this points to the importance of planning parts selection with how the car will be driven most of the time.
If this were my car with the listed parts/pieces there now and looking for a little more guts I would research the valve springs to see if they are matched to the cam, add a shift kit to the trans, some intake port work, and look at my timing, I also prefer long tube headers for the low end torque on the street but it's a personal preference thing too.
These are just my opinions and not based on any real mechanical experience.