Hi. If a '75 164 is any indication (and many cars are limited by their chassis, not necessarily their engine size), I can offer that there's a plaque on the front passenger-side (left) fender in the engine compartment that includes various specifications; included in the list of things is the maximum towing capacity (btw, I have the BW-35 automatic). It indicates a mere 2,000 lbs.
You may have that plaque there, too.

I only say "mere", because my 240's (with smaller engines) with AW70's all are rated at 3,500 lbs (assuming trailer brakes which I don't have, and a transmission oil cooler which I do have); albeit only 1,500 lbs if I don't have both of these things :-).

And the reason that I say that sometimes the rating is based on the chassis, and not the engine size, is that, for example, the VW Taureg has the same 7700 lb max tow load, and the same 615 lb trailer tongue limit, whether it has a puny V-6 or a larger V-8 gasoline engine, or even the monster torque, giant V-10 diesel engine. So not always, but sometimes a tow rating is chassis limited (and sometimes it's engine, transmission, or axle ratio limited, instead).

Anyway, look for that plaque, if you don't have the owners manual.