Here's an update on my 300D after yesterday with the mechanic:
1.Valves adjusted - weren't out by much
2.Timing was at 20 degrees - he set it back to factory 24.
3.Someone "not in the know" had played with the vacuum system - he spent an hour getting it back to specs. The tranny shifts much better now - not perfect - but I can live with it!
4.NOW THE BIG ONE: the car was originally from California. The injection pump was rebuilt at the same time that the engine was a few years ago. Whoever rebuilt the pump put it back to specs for California. My mechanic reset the pump to factory specs for Canada (where I live)--something to do with the governor I think.
Anyways, the car now performs equally as well as my old '75 300D. Drove up the longest hill in the immediate area - was at 80mph at the top - with more "jam" left if I wanted it!
I asked the mechanic if "tweeking" the pump will affect my mileage. He said it may even go up a little. That would be good, because I was only getting about 30 mpg (approx. 24mpg in US gallons!)