Complex sentence: Power for the production models was originally provided by two GM Diesel 4-71 engines of 160 HP each connected by a fluid coupling because GM had never seen the need for a V8 version of its Series 71 diesel engine.
Split into simpler sentences: Power for the production models was originally provided by a pair of GM Diesel 4-71 four cylinder engines of 160 HP each connected by a fluid coupling. Two engines were necessary because GM had never seen the need for a V8 version of its Series 71 diesel engine.