W108/W109 did not have pneumatic suspensions (That wasn't available on mercedeses before the W116 450SEL, 6.9, which had a hydropneumatic suspension very similar to that developed by Citroën).
W108 had springs, W109 had air suspension and no springs. Both the W108 and the W109 were available with the round headlights.
But the car in the photo is the big M100-engine AMG-version (The 600 grosser-engine), and that is a W109, not a W108. On the normal versions you can tell the W108 apart from the W109 by looking at the chrome around the side windows. W109 has all chrome, while the W108 has chrome and paint. Besides, the W109 was only sold under the 300SE(L) badge, not 250S(E) and 280SE(L). The W108 was sold as 250S(E), 280SE(L) and 300SE(L). But the W108 and W109 have the same body, and they are essentially the same car.
As for engines, the W109 was the only one that came with the 6.3-litre engine from the much larger 600 grosser. The 6.3 was special order, and a lot more expensive than the other versions. the were the fastest large sedans in the world. 0-62 mph in under 7 seconds was supercar fast in the 60s and 70s, and still is very fast for a large car.
But the version in the picture is the specially built racing version. They were even faster, and in the so called "Red Pig", that actually finished 2nd in the 24 Hours of Spa in 1971, the displacement had been increased to 6834 cc, producing 420 HP. It proved a bit heavy on fuel and had excessive tire wear