From Wikipedia:
The SM was sold with three very similar, small, lightweight engines, all derived from the contemporary Maserati V8 fitted to the Quattroporte. Because of the V8 origin, this engine sported an unusual 90 degree angle between cylinder banks - a trait shared with the PRV V6.
The engines - always mounted behind the front axle were:
2.7 L V6 with Weber 42 DCNF carburettors, "C114-1" (170 bhp) (1970-1972)
2.7 L V6 with Bosch D-Jetronic injection, "C114-03" (178 bhp) (1973-1975 - Not available in the US)
3.0 L V6 with Weber 42 DCNF carburettors, "C114-11" (180 bhp) (1973-1975 - US only in 1973, rest of the world, automatic only in 1974 & 1975)