Contact Phil at Parts Shop, give him your VIN# and he'll get you the right belt (you're correct there are 3 options).
You may want to change the belt tensioner damper while you're in there if yours has the external damper.
You will also have to loosen the tension locking bolt - a 10mm hex socket work great.
To set the tension line up the arrow on the tensioner with the markings while tensioning the belt with the 13mm tensioner.
Hope this helps.

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1995 Mercedes E320