I'm planning on fiting the alloy arms to my 350sdl - have both steel and alloy arms in my workshop.
My guess is that the anti squat suspension is heavier than the standard one - despite the alloy arms.
Keep in mind any used parts will be at least 20 years old and will likely need rebuild. There are 5 bearings per side. A bearing supplier has quoted me $560 (CAD) for two radial bearings...you may want to change the linkage bushings - likely MB exclusive parts. There are some throwaway parts in the hub assembly...Emerg. brake cables appear different, ditto for the calipers which are mounted forward of the axle...

Tip for buying used: stay away if the steel sleeves sealing the joint connecting the arm to the hub yoke have rusted thru....The alloy will likely be pitted...also check for corrosion at the shock absorber mounting studs.
The brake shield and the emergency brake mounting base may be corroded beyond repair...