You will have to decide how you want to spend your money. A used engine is a possibility, but don't buy one without a warrenty. There are numerous dismantlers who will sell you one known to be running properly when it arrived. A rebuild will probably cost more, but you will have an brand new engine, for all intents and purposes, and with proper care, it will outlast the body.
The fuel distributor problem is fairly common, and is about the only repair possible to a fuel distributor -- no way to fix anything else. Bosch rebuilds are the only way to go other than brand new if that doesn't work.
The other problems are due to either serious overheating or poor maintenace -- the engine in the 190s is otherwise excellent.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!