if you take a cam off the pulley and put a new one ie performance one... does the cam only fit oneway onto the pulley? if not you could be all over the place?!
Yea, only goes on one way. On the pully, you'll notice a notch and on the cam, there's place for a woodruff key - A Woodruff key or half-moon key, is a semicircular shaped, removable key that fits into a matching keyway cut into a shaft, leaving a protruding tab. The tab mates with a matching slot on a device mounted flush upon the shaft e.g. a pulley.
That way you can't get your "alignment" incorrect.

Hope that helps.