The weight of a 350 Chevrolet small-block engine varies depending on the specific year of manufacture, the components included (e.g., accessories like alternator, power steering pump, carburetor, intake manifold), and whether it's a bare block or a complete engine.
However, a generally accepted estimate for a complete, ready-to-run 350 Chevy small-block is between 450 and 550 pounds. A bare block will be considerably lighter, perhaps in the range of 150-200 pounds.