The car should have fog lights inboard of the headlights. Some people fit the fog/driving(?) lights from the SEC model that has them in the bumper. I don't know what it takes to do that.

I'll reserve comment on lowering.

I believe there are two fuel pumps running in parallel. The fuel filter is right by the pump/s. Follow the noise to the pump/s which is/are by the right rear wheel.

There are several possible causes of vibration on acceleration. Could be as simple as motor mounts or as complicated as a bad torque converter. My limited experience with such says to check the drive shaft carrier bearing first. The exhaust pipes and drive shaft shield have to come off for access to the carrier bearing. The drive shaft has to come off to replace the carrier bearing. Between the transmission and the differential, an MB is nothing like any American car. The consensus on this forum is that on the road as well, an MB is nothing like an American car.

Internally regulated for fuel flow? I don't know what you mean by that.

The engine is fuel injected. Bosch KE-Jetronic. Version 3 probably on your car. It's basically a continuous injection system with mechanical and modulation of the pressure with some computer tweaking. Drive a stake through the ECU and you'll still be able to get home.

There is a pressure regulator in the engine bay that sets the overall system pressure, as well as an accumulator near the fuel pump/s that maintain fuel pressure for quicker starts... maybe for other things as well.

Sixto
91 300SE
87 300SDL
83 300SD