One precaution- - - -the clamp also sets the depth of the distributor housing in the block. Make sure the dizzy doesn't get pulled up as you're setting timing, as it can disengage the shaft from the oil pump and still have enough gear mesh to run the engine. Make sure the housing is pushed down to keep the distributor shaft firmly engaged into the oil pump slot.
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!