The next thing to do BEFORE you do anything to the fuel system is to pull all the spark plugs and do a compression test. The M117 engines have a known weakness with the timing chain guide rails. If the rails have broken it is very possible it has bent valves or a "holed" piston. They are "interference" fit engines and a loose chain can be a catastrophic event.

While you have the plugs out, check for spark from the plug wires. The transistor box is a known weakness on all the early Benz'es.