Yes, the block-mounted starters were notorious for the drive teeth bottoming out in the flywheel gear and making quite a racket. The shims moved the starter housing down, and away from the tooth gullets in the ring gear. The simple way to check tooth contact was to spray paint an arc of the flywheel teeth and shim until about 3/4 or a little more of the tooth depth got the paint rubbed off by running the starter.
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!