I've been rebuilding distributors for about 15 years and I've found that you have to match the distributor to the vacuum signal. Without a vacuum signal most units will give you 10 - 20 degrees of advance depending on which distributor you have. 20 degrees won't be enough for a 4 cylinder engine which usually needs about 40 to produce good power. You can advance the timing to compensate for that but you will have problems with keeping the idle speed down.

Vacuum advance builds with engine RPM while vacuum retard disappears as engine RPM increases. Some systems have vacuum switch over valves which may have been employed on your car but may now be missing.

If you can find a 190SL distributor which gives 30 degrees mechanical this could work for you. If you find that the fly weights aren't working properly there's a good chance someone used a screw that was too long while mounting the condensor and it bent the arms which hold the return springs. This can be fixed sometimes.

Excessive wear at the bearings, combined with advance plate wear and top shaft wear, will make your points close up at higher RPM's with resulting dwell angle loss as well as timming loss. 55 degrees of dwell means your point gap is kind of close and you might want to open them slightly.

Your distributor has to function properly or the engine will never run the way it should. Having your distributor rebuilt is a common and very much over looked detail during engine tuning and restoration of older cars with these ignition systems.