I'll have to take your word you've seen one. I'd like to see a picture of an unmolested 383HP where the pistons are proud or even with the deck. I've had three I personally owned or took apart: the original in my '70 Cuda, the original numbers block in a '70 Challenger, and the numbers matching engine in a '68 Road Runner. I took them all apart for the first time. All were .030-.040 below deck. All were factory stamped HP and had the correct HP parts. The decks on two of the three were taller than blueprint by .040-.050 thou. I'll add the 496 I just did - that was the numbers 383 HP from another '70 Challenger. In order to get the decks to blueprint height that block had to be decked far enough to remove 95% of the stampings on the pad (not by me - but reputable shop that rebuilt the 383).
So while the engineering design said they "were" the crappy execution made them "not".