Doc, the ones with shims usually bolt to the block, not the bellhousing. Since the pinion gear on that type of starter is slightly below the center line of the flywheel, shimming it further down keeps the teeth from bottoming out in the flywheel gear. The bellhousing-mounted ones generally don't give any problems. A sneaky trick to check tooth engagement is to paint a dozen teeth or so of the flywheel gear with a rattle can and spin the starter with the ignition disabled to see how much paint gets rubbed off. About a 90% tooth engagement with a bit of paint still showing at the bottom is ideal.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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