Complex sentence: The new car was based on the unitized chassis and body of the four-cylinder Humber Hawk, but with a 2.6 litre, enlarged in 1959 with the Series II to 3 litre, Armstrong Siddeley-based, inline six cylinder engine.
Split into simpler sentences: The new car was based on the unitized chassis and body of the four-cylinder Humber Hawk, but with a 2.6 litre. For the 1959 Series II the engine was enlarged to 3 litre using an Armstrong Siddeley-based, inline six cylinder engine.