The VIN stamping appears consistent with factory stamps in that location but of course even so the VIN doesn't indicate the car was a Z28 from the factory unless he has the original (legitimate) documentation and warranty book (P-t-P) matching the VIN, and even that wouldn't prove that the engine is the born with engine...
I've never seen a real DZ engine stamping as 'odd' as that one.... so that is VERY doubtful! It doesn't seem it was done with a gang holder.