some superbirds are NOT stamped on the core support.
50% of the Birds were not stamped on their core support - not sure why but mine was not. Also you have to go underneath the weather stripping on the trunk lip to find the other VIN but I do not want to disturb my weatherstripping since trunk is watertight.
You should be able to make out the reverse impression left by the stamps. I know I can on my GTX.
Mine were stamped on the radiator side of the yoke.
I found the vin# on the trunk lip of my Superbird today, It does not have one on the radiator yoke. Thanks for the input.
Steve