All that I can say, is when I brought my 1971 Plymouth Duster 340 to the Carlisle Mopar Nationals, the "incorrectitude" of my engine was viewed as a B.F.D. (Big Friggin' Deal) amongst the spectators.
It didn't matter that it still was a 340 cubic inch engine. The car came from the factory with the 340, and my car was still a 340 (or close to it, after being slightly bored out from its 400+ hp rebuild).
It was just that it was a "N.O.M." (Non-Original Motor), or not "Numbers-matching". Furthermore, the 340 engine block was a 1969 casting, not a 1971 casting that would match the year of the car. Even though the castings between those years was very similar.
Sooo...this was all viewed very badly. Even the person who eventually bought the car from me noted the engine "incorrectitude".