Every era has its must-have engine development. Sometimes the idea is adopted more from fashion than engineering neccessity. During the sixties, the must have was DOHC. In the UK, Lotus took Uncle Henry's humble four cylinder and turned it into a ball of fire with a DOHC head. You could by a twin-cam cylinder head for a mini.

Bear in mind, however, that materials technology was under developed at this time. What is possible now with rocker arms and push rods, was just too complex for the steels and irons available in the sixties. The mass of the drive train and the acceleration needed for shorter duration cams was too much for all this valve gear. A cam placed directly over the valves eliminated a whole lot of mass. Thus, for an efficient cross flow head with sort duration valve timing, direct acting cams (requiring DOHC design) were the engineers solution.

Remember that MB always had relatively high output engines that lasted a long time. This was achieved by using the best design techniques, as well as care full engineering and assembly.

The quality of materials, precision mass production using CNC equipment, oils, electronic controls, all play their part in changing engine designs.

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Cheers, Neil