Complex sentence: The 1,816cc diesel unit came from a company established by Peugeot to specialise in the design and manufacture of diesel engines, and the same unit had, since 1959, been offered in the Peugeot D4.
Split into simpler sentences: The 1,816cc diesel unit came from a company established by Peugeot to specialise in the design and manufacture of diesel engines. The same unit had, since 1959, been offered in the Peugeot D4.