How to verify if an A-body is numbers matching?

AWESOME INFO! That is exactly what I was looking for! I think I have a good idea of how to evaluate what I am looking at, but I really wanted to consult FABO members so that I can give this car my full attention.

Again, this car seems great on the surface. We will see how things pan out after I spend some quality time in person with the car on the 25th.

Anyone else care to chime in? I know that I should check the fenderwells, the rockers and rear quarters for rust. Additionally, if there is undercoating on the car (wheelwells, undernearth) it should be body colored, correct?