Thank to all of you for your replies.
Sometimes I don't think things through or I would have realised that the top weight replaces the weight removed by drilling, and that up to 5 oz should not require a balance hole, depending on the depth and diameter of the holes.
I am wondering about the ball reaction with different levels of top weight. and the label leverage drill. Has anyone done any experimenting with this?
Thanks for any replies.
--------------------
OnlyBowling