What are the numbers on front of a Chevy small block?

The numbers cast into the front of a Chevy small block engine (on the block itself, not the intake manifold) typically indicate the engine's casting number. This number identifies the specific block casting, which can tell you things like the year it was made, the displacement (e.g., 350, 327), and other features. There isn't a single set of "numbers" – it varies depending on the specific engine.