best bolt ons for a 318

I want to get the most out of my 318 as possible.

What are the best "bang for your buck" bolts-ons that I could do to add some horsepower to this motor?

Here is what I have so far....

headers, dual exhaust, Edelbrock intake, Holley 600 4 BBl, Mallory electric ignition, flowmaster mufflers, manual valve body 904 and an 8 3/4 rear end with unknown gearing.