Several of the cast/chromed alloy clamps being sold by the 'dress up' kit suppliers have no real strength, & deform when tightened. Find the original steel version, paint it blue & fit it.
Check that the shaft is not running dry in the dist housing from lack of
oil, this also can pull the dist housing in the retard direction in use. Mark the block/dizzy with a punch to have a quick reference to look at in the future.