The wheel/tire size and offset is the problem, the OE wheels & tires do not rub even if down on the snubbers.
The changed wheel geometry can also put more leverage on the suspension if it is out further than normal, and cause the car to sag.
If you're sticking with the wheels & tires you have, you can look into fender spacers in the front, the rear is probably not a problem unless you have a serious offset change (I'm running 16x8 ET40 with no rubbing regardless of load for example, stock body). The 500E with wider fenders ran 16x8 ET34, too tight on the front for me without spacers.
I also believe that the later 124s have the fenders rolled, and the early do not. Might check into that as mentioned in the FSM how to roll the fender lips for wider tires.
http://www.peachparts.com/shopforum/showthread.php?t=219584
Nice looking cars BTW.