The 84 Euro 500SEL is simple K-jet similar to US models 450 from 76-79. System manuals for these cars will explain the system. The only electrical for the fuel system is the fuel pump, warm-up regulator heater and the cold start valve. Very simple from that stand point.
Cars brought into the US were either modified to meet EPA standards or were exempted under the "service person exemption". This exemption allowed military people to bring home a car that they owned while stationed abroad. These cars still had to be modified to DOT standards but could be exempted from EPA regs. These cars had to be 5 years old before shipment. Since the whole grey market thing ended in about 86 or 87 a 84 model likely had EPA mods.
If you have no emission testing in your area I would make the car run as it was designed. If you have testing....move, or sell the car.
Bosch Master, ASE Master, L1
33 years MB technician