Yes, it is. A "Not Original Motor (NOM)" SS396 is of considerably less value than a numbers matching car.
This car's engine stamp is not legitimate; if the engine had been replaced under the warranty the car would have receive a replacement block that was stamped (
at the engine assembly plant) with a code similar to "CE012345 (where "CE" stands for "Chevrolet Engine" -- there's more to the code but that's not important at this point)." What is important is that a "Matching Numbers Engine" serves to validate the car as being a real factory SS396 (and not a clone).
ALSO the fact that someone falsified the engine stamp calls into question the car's Build Sheet (i.e. is the build sheet real or is that faked too?) and the ProtectOPlate.
and it's bid up to almost 26 grand!