[66 L78 ragtop]

I agree that its not a good idea to bank on anyones recollections.
JD ad was for 425hp rated 396 motors not 427. He basically sold 66 L78 Chevelles that were rated 425hp at 6400rpm vs 375hp @ 5600rpm. Same engine. Some people say that the different hp ratings were based different sized cams, but this remains to be proven

For unreal:

The 66 L78 and 69 L78 were completely different engines.
Different blocks, pistons, cams, intakes, heads, and different carbs. The only thing they shared was the crank shaft. Although the cams had the same part numbers, they had different intake and exhaust durations.