[Enoch]

I have restored 5 '66 Corvette's w/ L-72's Serial #'s from under 1000 tru 20,000. No difference in any parts of the motors were found. I have heard 2 stories as to the reason for the 25 hp "de-tune".
First Insurance reasons.
Second Chevy execs. knew the L-71 was coming out the following year and they thought it wiser to go back to 425 and go up from there than up from 450 with the rating of the L-71. Also at this rate the L-S6 would have to have been rated around 500 hp.
As a side note all 5 motors were run on the dyno after stock spec rebuilds and they all made between 470-480 hp and 480-500 ft lbs of torque.