The timing ring on the stock balancer is just pressed on. You can pull it off and press it on in a different spot. I had gotten a new balancer several years ago, and it didn't come with a timing ring. A mechanic was working on my car at the time (this was before I started doing all my own work), and he pulled the timing ring off the old balancer and pressed it on the new one, but apparently missed getting it into the right spot by a few degrees.
A post to the old mailing list (from pudd'n I believe) said "The edge of the ring should be lined up perfectly with tdc mark on the harmonic balancer. With age they seem to move. They are only pressed on."
Mine didn't look like that. Mine looked like this (the string is in the balancer 0 deg mark):
http://pages.prodigy.net/buickv6/CarStuff/balancer1.jpg
It looked close, but not close enough. The difference between 22 deg and 18 deg could be significant at full boogie after all.
Now I never got to check the timing with that method I described while the balancer was set as in the picture (I was in the middle of doing a cam swap I think), but I thought there might be a problem, and I didn't want to put the balancer on, check it, find a problem, and have to pull it off to fix it. So I risked pulling the ring off, moved it to where I thought the right spot was, and installed it, hoping I wasn't going to have to pull it apart to set it back where it originally was
So I don't know just how many degrees the ring was off in that picture. I do know that I moved it, checked it when the car was running again, and it was spot on at that time.
John