The alternator can run in any direction. It's an AC device. The rectifier plate will convert it to DC to power the car and charge the battery. Direction doesn't matter at all.

On any given engine, the belt will only turn the alternator in one direction anyway, regardless of how it's routed, so it's a moot point.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]