put this picture in your mind...
see that yeller dot?
on the top side of it is a scribed line
and there's another one on the opposite side
line 'em up with the top of the head
see the alignment pin right next to the cam gear mounting hole?
it goes there and no where else.
notice one more thing...
see how the right side mark is up a bit?
that's cause it's a used chain
the slack is taken up on the left side
so when you got a stretched chain the alignment will be off a little bit.
and that's ok, just don't let that cam adjust plunger fall out or they'll be picking you up with a shovel.