The Super Snake engine was UNDER 500 hp. A couple of factors were responsible for that. The aluminum heads C5AE or C6FE versions ( not tunnel port) used LOW RISER valve sizes ( 2.090 and 1.660) not the 2.190 and 1.73 used in iron medium riser heads. This was done to keep the larger valve seats from falling out of the aluminum heads. Next was the cams . They used smaller cams as they weren't drag racing. They were also given a 6,200 MAXIMUM rpm redline despite over 7,000 rpm capability so they would last 24 hours. The compression was 10.75 as listed in the Experimental Engine Engineering build books. The technology wasn't there in '67 to build an endurance engine with 600 hp. The whole Idea of the "light weight" 427 was to provide more usable hp at the sma weight as an all iron 289. With the Magnesium intake , aluminum heads , aluminum (or magnesium ) water pump, and aluminum center harmonic balancer , they were close but with almost 100 more HP at 1,500 less rpm.
It's amazing hoe the HP numbers have grown over the years.
Randy