Engine size

[Lamar Wadsworth]

The first character of the serial number tells you what engine it had from the factory. 7 indicates '57 model year. N indicates Norfolk VA assembly plant. G tells you it's a Custom 300. Now, unless you know the history of the car from day one, don't assume that the engine in it matches the serial number plate. All Y blocks look pretty much the same externally, so check casting numbers on block and heads to be sure of what you have.