The oil pressure sending unit on a 1979 Chevy Silverado with a 454 engine is located on the driver's side (left side) of the engine block, near the distributor. It's a relatively small unit, often with one or two wires connected to it. It's usually mounted fairly low on the block. However, the exact location can vary slightly depending on the specific engine configuration.
To be absolutely certain, consult a repair manual specific to your 1979 Chevy Silverado 454. A Haynes or Chilton manual will have diagrams showing the exact location and can help you avoid confusion with other similar-looking components.
