My mechanic uses compressed air to hold the valves up and just displaced the rocker arms from under the cam. Very easy, since you have hydraulic lifters and not the solid lifters on my 280SE!
I think all the replacement seals are the small size. They work fine. Replacing them will eliminate the oil consumption problem.
Check your "radiator" cap, too -- it's often dead by now, and not holding pressure or, more rarely, not releasing vacuum!
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!