I see on the internet that a lot of people wonder what "lightweight" small block Chevy heads look like. Below are some pictures of the heads that my 350 came with. They are casting number 462624. The '6's often look like '8's, but the casting numbers 482624, 462824, and 482824 do not exist. There are other "lightweight" small block heads with different casting numbers, however.
Lightweight small block Chevy heads have scalloped sides. Note that the work bench top can be seen between the head bolt holes. Avoid these types of heads, because they crack easily, and because they don't make any horsepower anyways.