1975 Mercedes 450SEL ECU

I have a mint condition 1975 Mercedes 450SEL (body 116033-12-032662, engine 117983-12-032803) with only 95,000 original miles. It has had everything possible done under the hood, short of a new engine, and it continues to idle ruff and perform inconsistently. Engine facts: good compression, no vacuums leaks, all new injectors, all new engine sensors, new plugs and plug lines, new distributor cap, rotor, and points, new coil, all new vacuum lines, new fuel pump and filter, new EGR value and air-injection pump. Timing set to TDC and dwell at 31.5 degrees. The only thing left is the electronic fuel management computer, which seems to be functioning ok. Unfortunately, 1975 was a horrible year for cars because of the newly established emission standards. This is especially true for cars sold in California, USA. Mercedes didn't escape this problem and they created a real Frankenstein smog system for my car, which I presume included the electronic fuel management computer. My questions: (1) is there an after market computer management system that I can install on this car to help it operate better, or, (2) is there a carburetor/manifold replacement that I can use? Any suggestion would be most helpful.