[PxTx]

Sounds suspect. A street legal GM car has to be submitted for an FTP (federal test procedure) to ensure it complies with emissions and such. The cost of this FTP is very expensive and would not happen for a 1 of 1 car these days.

There may have been a time where GM could stick in any engine they wanted into a car and get away with it, but not in a long time. If they car has a 454, it will be by a 3rd party group, like Nickey. If the car is a special GM build, it will not be 1 of 1 AND street legal (meaning you can register it).