318, 383 or other? Which one

Header wise, it's tti.
What is your rear suspension consisting of?

For $1500, first I'd do a cal track set up in full with some MT drag radials. Then I would do tti headers into 2-1/2 exhaust ending at the rear axle instead of the full exhaust kit from them. As you may not have enuff money for the full deal to the bumper.

What exact intake manifold do you have. With the sound of this build, you'll need a RPM or M-1 single plane to get the job done and done well.

Any mods to the AFB?