The problem is that the various hook rating scales have changed so much since that time.  At one point, 10 was the top and they had to re-rate the balls every couple of years or so and eventually upped the top-end of the scale as the newer balls kept getting stronger.  Manufacturers all had different scales so comparing one company to another was difficult unless you used the ratings by independent evaluators like Ball Reviews or Lichenstein (?).  So trying to rate an old ball on today's scale system is difficult.  I don't know if they even go back and rate old balls to see where they fall on the newer scales.  You could email the people at bowlingball dot com who have the Perfect Scale and see if they know.