Special L78 Nova Code Under the Heater Core Cover?

[92646]

Somebody called and was asking questions about my 1970 L78 Nova that I have for sale. He asked if I had seen the special 3-digit code that was stamped on the firewall under the heater core cover. I thought he was talking about one of the hidden VINs but he said there was a specific code for a L78 Nova in addition to the VIN stamp. This was news to me has anybody else heard of this code? If so I know what I will be doing this week end.
Mark Sheppard