Check the first six digits of the VIN/chassis number. It'll tell you exactly what you have.
In any case, the M116 was available in the US from 68-71 in the 280SE 3.5 coupe and cabrio (W112) and 300SEL 3.5 sedan (W109). Maybe the W112 was available through 72. The early US 350SL had the 4.5l M117. Those cars were recalled to have the badge upgraded to 450SL. While popular elsewhere in the world, the real 350SE and SEL (W116) as well as the real 350SL and SLC were not officially sold in the US.
Try to locate a factory owner's manual for the car you have. www.schiffeuropean.com
will probably have an English owner's manual for your car. You might get lucky on ebay. Take it with a grain of salt as your car might get a UK spec manual for your (hypothetically) Austrian spec car.
I have a hardcopy M116/7 engine manual at home. If there's anything I can look up for you, let me know. I'm pretty sure tune up specs are in another volume of the MB shop manual series, though.