Hi everyone,
The Saab setup is, I believe, desireable for OM61x or M117 cars with V-belts. You can't use a late-model serpentine belt alternator on a V-belt car, that's why the Saab units are handy - if you can find one.
For Mercedes with serpentine belts and dinky 70-90A alternators, the 143A or 150A units are the hot ticket. It's a straight bolt-up BUT there are the following caveats:
1) You need to use your original pulley! Sometimes it's nearly impossible to get the pulley off your old alternator. In that case buy a new one for *your* car and swap it onto the 143 or 150 unit. Costs about $30 for a new pulley. I had to do this on one of my alternator upgrades.
2) You may need to re-clock the big alternator. That means removing the 4 screws that hold the two halves together, gently pry it apart, turn the rear half so the big battery terminal is in the optimum position for YOUR car, and screw it all back together. On a rusty used unit, this can be a real chore. On a super clean used, or rebuilt, this is easy. Shouldn't be any problem on a 6-cyl car but on an M119 engine, even with re-clocking the clearances can be really tight - trust me, I did it on my E500 with a 150A unit.
3) You need to toss the stock wiring harness to the battery and fabricate your own with heavy cable. This is not difficult, but if you're not handy with large electrical connectors, have it done at a pro car stereo shop. Use 4ga at a minimum, preferably 2ga, and 1/0 (pronounced 'one-ought', or zero gauge) is about the biggest you can realistically use. Custom battery terminals are required, etc.
4) The very late model 150A alternators, as shown in that auction linked above, have a different voltage regulator. I do not know if these will work with older cars (1986-2002) or not. They may, they may not, until someone tries it we'll probably never know. I have the part numbers for the special 2-prong VR connector required, if anyone wants to experiment... they're only a few bucks. The auction closed ridiculously cheap! Too bad I missed that.
Photos of my installations are here:
http://www.w124performance.com/images/W124_stereo/alternator/
Best regards,