Just to be sure are you speaking of towing the Mercedes from the Front behind another Vehicle or do you want to pull a Trailer.
If you want to pull a Trailer that is light weight Trailer Hitches & Vehicle Accessories (800)298-8924
Curt Trailer Hitch 11614.
But, this other Trailer Hitch appears to be stonger DA217336 Dalan Hitch but also does not appear to be sold anywere.
Back in the 1970s I bought a generic Tow Bar to pull a Pickup Truck during a move. The Bar was set up for a flat Bumper and was in fact made for a Jeep at that time.
I had a spare badly rusted Steel Bumper for the Truck that I swapped onto the Truck and I drilled the 4 holes into that and infact that Bumper is still on the Truck.
Questions is the 78 240D Bumper strong enough to drill holes in and tow the Care and do you want to drill holes in the front of the Bumper? Next question is is what holde the Bumper in place strong enough to remain attached to the rest of the Car when you tow it.
Also if you tow your 240D the stock Transmission you have does not have the rear pump in the Transmission. That means you need to detach the Drive Shaft so the Transmission does not turn.