The W126 front rotors are bolted to the hub from behind. It is necessary to remove the hub to change them.
I just clamp the rotor in a large bench vise, and have never had too much trouble getting the bolts out with a 24" breaker bar and 1/2" drive 10mm allen. I'd not use a 3/8" drive, too light.
Make sure the hug and rotor mating surfaces are nice a clean -- a chunk of rust in there can make the brake pedal pulsate!
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!