I've never heard of using shims on a bellhousing-mounted starter. The ones that bolt to the block near the oil pan rail sometimes need to be shimmed to avoid the starter pinion teeth bottoming out in the flywheel teeth. A good way to check tooth engagement is to spray-paint the pinion gear teeth, then spin the starter for several seconds with the ignition disabled and see how far down in the tooth the paint gets rubbed off.
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
Love your enemies and drive 'em nuts!