Be careful messing with the 1987 300TD cooling system. Those heads do NOT tolerate overheating one bit - you did know about the head issue on those cars, right? If not, search the forum.
There's not room for dual 12" fans on the W124, the radiator isn't wide enough. A single 12" isn't adequate, IMO. Try to find a single 16". The depth is quite limited as well. Your test points out what I keep trying to tell others, that the fan really DOES do something on the freeway... everyone seems to think the ram-air effect is plenty but it is not.
The alternator upgrade is cheap and easy - I would NOT skip this step!!! The stock alternator can't even keep up with the basic electrical loads at idle (lights, ACC fan, etc...)
