Hi Mario,
Its just the tooth count, best thing you can do is wip it off when you go to buy the new belt to make sure the one they give you and the one you have match.
The head skim should cost £20-£40 to have done, some times its a bit more due to the welding needed to correct damage caused by rust to the water channels (precisely why you should be running red coolant I expect)
I was lucky I suppose and didn't need that. If I hadnt of needed a new Rad fan I would have had change from £100
I replaced:
New cam belt, new aux belt, tensioner, HG and stretch bolts and other gaskits, coolent, oil, new Rad fan as other was MIA and had head skimed