Good idea and really easy too!,find a wreck W111 from 1965 or newer and it will have front disc brakes,but the older type of mastercylinder,or track down a wreck w108 chassis car,engine size doesn't matter.This will have same front end but bigger disc brakes and the newer master cylinder/booster assembly.
The front assemblies can be swapped around,and it always pays to change the two rubber mounting bushes on the crossmember.
With this model you can swap over the diff assembly to get rear discs,BUT,and it's a big "BUT," there is body work involved here.The rear disc brakes require a couple of mounts to fabricated for the caliper hold down/anti dive arms. The diff width etc is the same and will bolt straight in,the only down side is the ratio will be higher from the later model gas car.It may work ,but I suspect it will be too high geared for the little diesel.You can swap in the ratios from the 190 into the w108 diff.Big job.All in all it's a leggo job.[

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