Hello!
Looking in my references there is no special tool that is used in order to line up the timing belt. Only a special tool used to check the tension of the belt.
Here are the pictures of the alignment marks.
NO... I don't believe there are any marks on the camshaft under the valve cover.
And no... the sprocket should be able to be changed from the camshaft.
NO... but all you will have to do is just call the dealership to get the part number.
If you look at the diagrams, both of the sprockets have marks on them. So if for some reason you cannot see a mark on the old one, just get a new one.
ASE MASTER TECHNICIAN
VOLVO TECHNICIAN ASE MASTER TECH WITH ADVANCED LEVEL PERFORMANCE