Big Block Question

[Stubbadub]

I have 2 stupid rookie questions. I'm looking at purchasing a Nova that the drivetrain is removed from (engine, trans, and rear). The owner is stating that the Heater Core is for a big block and that it has a 3/8" fuel line. My questions are, how can i verify that by looking at the core (what should i look for to tell if it's a big block core) and are there any other indicators i can look at to verify that it was once a big block that was in the car? The VIN is no help, though it does code to a V8. Any advice is greatly appreciated.