The ALDA just sit on top of the actuator in the IP. Held on by a captive nut. Best to use a pair of small adjustable wrenches to get it off if you don't have some "shorty" wrenches -- space is tight (duh, I don't need to tell YOU this!). You will need to remove the windshield washer reservior for access.
My mechanic says he has never had to adjust the ALDA on a 603 -- if you don't get a little smoke at full throttle, check the overboost protection switch and boost lines before digging into the ALDA -- a clog or open overboost switch will reduce power quite a bit. Old tired hoses will give the same result, as will a plugged trap oxidizer, if you still have one, or a tired turbo. To adjust it, you will have to take it off.
The glowplugs can be removed using a deep swivel socket -- the kind where the socket is one side of the swivel. You will need one for the wire nuts and one for the plugs. Use a bit of paper to hold the nut in the socket when you put them back on.
I plan to do the head gasket on mine when the weather warms up, after I check to make sure I don't have a coolant leak. I replaced the thermostat this fall due to low engine temp, and will need to check for leaks there before yanking the head. The only symptom I have of a bad gasket is a slow coolant loss.
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!