I might consider the 120A alternator if I needed to change mine alternator anyway, especially since cheaper than the $150 I paid in 2001 for a NAPA one. I like the stud outputs, which is more reliable than the spade connector on my 85 300D, plus no sense having 2 output spades & wires like the factory design. Otherwise, my battery recharges fine w/ the factory 65 A alternator, so I don't see the necessity.

The headlights should work fine off the battery alone. If too dim, there are probably issues with corroded connectors. I don't see a need to keep up with the glow-plugs while cranking. Indeed, that is silly. A larger alternator would just load the starter motor more while cranking, causing more draw from the battery. It isn't a "perpetual motion" machine. On the same thread, why run the alternator output to the starter? Indeed, it would be nice to disable the alternator while cranking, which I think some car systems do. If your present alternator keeps the battery charged, a bigger one would just risk smoking wires.