If you got the engine number from behind the left cylinder head then you have a 3.5l D-Jetronic engine as MB DOC says.
A 116.983 engine would have come in a 72-75 350SE/SEL sedan. A 73-75 450SE would have a 117.983 engine.
One way to tell what car you have is by the VIN or chassis number (on the door pillar, radiator bracket, elsewhere on a 116?). A 450SE is a 116.032, a 350SE is a 116.028.
BTW, if you have a 116.983, it'll make more power than a US 450 will ever know. And a Euro car will have a 4 speed transmission.
In later years, 116 would also be the 3.8l and 4.2l engines, and 117 would also be the 5l and 5.6l engines. But none of these engines use electronic fuel injection. But this is a tangent.
78 450SEL with 117.985-10 engine (Euro MT) (sold)