'89 300e

A new owner (2nd) of a prestine 1989 300E from an very mature lady. 54,000 original documented miles. I have some questions and problems. Where exactly is the engine #? When replacing the front drive shaft rubber ring do I also need the mounting hardware? What do I have to do to unlock the radio, it has 4 dashes accross the display? ABS and SRS lights are on. (did not come on when I test drove (10 miles) before purchase. Does engine require filter with check valve? What kind of gas mileage?
What are procedures for switching A/C to R134a? What RPM should you see at 55mph? Can you reset engine timing for less than premium gas? I have a Service manual on CD coming from Mercedes.