The bracket that holds the vacuum advance bolts to the engine block, with a slot in it that allows for a limited amount of timing adjustment available. For more radical movement, loosen the pinch clamp, which would allow for 360 degrees of movement. The motion of the distributor housing caused by the vacuum advance cannot, and should not be restricted- - - -that's a "feature-- - - -not a bug"!
LOL!
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!