I just bought a Bosch AL74X from Summit racing for $95 with a $5 or $10 core charge which I thought was pretty good. It will need a spacer to use the original 230SL pulley and I haven't tried it in my mount bracket. I got a later style mount bracket from Naj, and don't know if the bolt/spacer configuration is the same.
This is my original bracket and mount, it was yellow cad plated, and these are the various rubber washers and cups that were used. All looked pretty original and stock to me, and I'm certain it is the original alternator.