Instinct says the tensioner will draw the right cam CCW (in the retard direction). I would hold the left cam still and turn the right cam manually CCW to take up any slack in the chain the short span between cams. You should be able to get the right cam to line up this way as a check. Then install the tensioner and check again.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD
78 450SEL (sold)