Most of the aftermarket timing gears have multi-keyways in them for this purpose. The Cloyes timing sets we used in all the 292 dyno testing recently were all degreed in, in this manner. But before you actually start just assuming you need to advance the cam, you need to degree it in first to see where you are at to begin with. If you are using an aftermarket camshaft, you can simply look at the cam timing specs on the card to determine what needs to be done. If you have a camshaft of unknown specs and no cam spec card, it is still fairly easy to determine how to degree it and at what point it will yield the best performance, even with no manufacturers data. This latter method is a little different than the traditional centerline method and involves a few more steps to perform, but it puts the cam in where it will make the most power everytime. However, since the Cloyes timing sets for the 6's will only allow you to move the cam 4°+/- from straight up, you might not be able to dial it in and get the same results as timing sets that allow you to move the cam in 1° increments as in SBC, for instance.
There's no such thing as too much cam, only not enough engine!
12 Port Head Manufacturer