Looking at one web parts site I see one type for engine #'s up to 12-179741 and another for engine #'s from 12-179742. I suppose one uses the push-on connnector; the other fastened with the small nuts/washer(s).
Here's the details from one place. One of the photos shows the AL potion of the part number; the rest is indiscernable.
This might help you in dealing with the indy.
Did you take the orig. alt. to the indy to match it up the first time around? Doesn't sound like it.
http://catalog.eautopartscatalog.com/smittys/sa/wizard.jsp?partner=smittys&clientid=sasponline.com&baseurl=http://www.sasponline.com/&cookieid=1AA11VG8C&year=1989&make=MB&model=300-E-002&category=F&part=Alternator&appEngines=_any