The casting number appears to start with a zero. Around 1981 I bought an aluminum big block intake at a swap meet. I paid either 50 or 75 bucks for it, I forget. Got it home, checked it out and realized it wasn't for a big block Chevy, it didn't quite fit. I ordered a 409 intake gasket set to see if it was for a 409. Nope, not right either.
The casting number started with zero. No internet in those days to search, so magazines, phone calls etc and I finally was able to figure out I had bought an intake for a Mystery Motor as they were called. I contacted an expert on those engines and he told me all the experimental and super low production stuff at GM had casting numbers starting with zero.
