Steering coupler should be exactly horzontal with the wheels pointed straight ahead, steering wheel level. Usually a locking tool to hold the box at this point, but you may not be able to find it or use it (no room on the W108).

You can spray some spraypaint into the "slot" on the coupler to mark the shaft for the gap, then install the new one so the paint is in the gap, or put some paint on both coupler and shaft, then put the new coupler back to back with the old one and transfer the mark by painting the new one in the same spot. Anything so that you can put the new coupler on the steering box on exactly the same position on the splines as the old one.

It may be eaiser to move the steering box -- three bolts and it's loose, no need to disconnect the steering linkages. Just support and slide forward.

Peter

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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!