Every dial gauge will need the sleeve that threads into the port on the pump and attaches to the body of the gauge. Some sleeves are a single piece, some are segmented for use on various engine models. Google image search: VW diesel timing gauge.I use this: http://www.harborfreight.com/1-inch-travel-machinists-dial-indicator-623.html , with a sleeve.You'll need all the bits, so you might as well get a kit.
...BTW your Bieber avatar is awesome.-Malone
Paint marks scare me, that is not how to time a VW diesel. Please tell me you have it correct and you have looked at the Bentley and vince waldon's how to site?
The cam belt won't matter. It is infinitely adjustable.