GT40P, GT40, AFR, BRODIX, EDELBROCK, HOLLEY, WORLD, CANFIELD-FULL RESULTS, AIRFLOW DATA, POWER DATA, CHAMBER VOLUMES, PORT VOLUMES, VALVE SIZES, VALE WEIGHT & SPRING RATES! ALL THE DATA YOU WANT TO CORRELATE IT TO THE CHANGE IN POWER. HOW MUCH ARE HEADS WORTH ON A PERFORMANCE 306 FORD? IT'S ALL HERE!