Jim F's trick about the fan resistor is for M119 engines (and probably M104 as well as M120) but I don't believe it will do anything on an OM60x or M103, which use simple on/off switches. You can add a manual switch to turn the fan on when desired but I haven't found a need for this yet.
I've been wanting to research the SPAL fan a little, but in search of power gains on the M119, not for improved cooling. It may provide better cooling at idle, but I'm afraid it will be noisy, and I'm not sure what the CFM rating is. A big alternator is required but we've already proved that's a simple upgrade.
Besides all the usual stuff to check when your engine is running on the wrong side of 100°C, also check the space between the radiator and condenser, in case you have a nice big dust bunny like this one (which was hiding behind my electric fan) :
