Chevrolet's 'W-Series' 348 and 409 engines from the late 50s onward ... cylinder head was a big change that would not only improve performance but also preview the later Mark IV 427 that would ...

The Chevrolet 348 and 409 V8 engines were known internally as W-series engines ... numerous high-performance versions would become available as the 409 V8 engine evolved through its short lifespan.