Power is in the heads PERIOD! My car went from 13.80 to 12.80 going from 915 casting 2.02 heads to OOTB 63cc edelbrocks. No other changes were made.

My motor is just a basic 9:1 340, with a decent set of heads on it.

IMO don't mess around with anything iron/factory unless you already have them. I sold my heads I took off for $300 so I basically have $1000 into my new heads, my car makes way more power, and I took weight off the nose of the car.