No need to change engine oil if it is not very black. Transmission oil is good almost for life, but change if it smells burnt. Rear axle is good for life. Definitely change coolant and brake fluid. In my 300D's, I use Evans Waterless coolant and DOT5 silicone brake fluid, both of which last forever (no corrosion).

When you do change engine oil, always use "CJ" rated "diesel" oil. It has more detergents to suspend the ample carbon from a diesel. Many classic owners use diesel oil in their gas engines, since higher quality and more zinc to protect lifters. You can use regular "gas" oil in an emergency. The Owner's Manual list weight choices, pretty much the same as for gas engines. 10W40 if you live in the South or 10W30 up North. Hedge slightly thicker if the engine is worn and shows much blow-by puffing w/ the oil cap off.

Transmission oil choice is in dispute here. Many use Dexron III (GM), which is also cheapest. I have used Mercon VI (Ford). You would probably be OK with any type. Many racers and classic owners use Type F (Ford) since it has more friction for faster, harder shifts, and thus less clutch plate wear, but not as comfortable to passengers.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans