On my '69, I was able to see the hidden VIN under the cowl panel without removing the panel, by using a bright light and viewing thru the cowl vent slots... From a 'legality' of ownership perspective, he should at least verify that the VIN he's considering purchase of is actually the original VIN of the car by checking at least one of the hidden VINs. It appears he's not interested in a 'matching numbers' Camaro, or one with 'special mfg features', but just wanting a nice Camaro to drive. And the car he's considering admittedly is a 'modified' car. that said, and if he understands that then the only things he really needs to verify are:
1) Is the VIN correct (this is a legal issue wrt ownership of the car)...?? If this isn't true.. then RUN..
2) Does the car exhibit signs of improper rust or wreck repair?
3) Does the modified car have the features he desires in a driver Camaro (ie. engine, trans, brakes, interior, etc)?
4) Were the modifications performed to his satisfaction?
5) Does he LIKE the way the car looks and drives for the price ...?
IMO the trim plate only states how Chevrolet built the car initially, and once a car is modified (and if the owner is happy with it), it really matters now at this point in time.