Even if the weights are within USBC legal limits you've altered it and changed the weight of the ball per the last sentence below.
From the USBC Rulebook:
Section 2. Drilling Specifications
a. Holes - The following limitations govern drilling holes in a bowling ball:
1. Holes or indentations, not to exceed five, for gripping purposes.
2. One hole for balance purposes, not to exceed 1-1/4 inch in diameter.
3. One (1) vent hole to each finger and/or thumb hole, not to exceed 1/4 inch in diameter.
4. One mill hole for inspection purposes, not to exceed 5/8 inch in diameter and 1/8 inch in depth.
b. Balance - The following tolerances are allowed in the balance of the ball:
1. For a ball weighing 10.01 pounds or more:
a) Not more than three ounces difference between the top of ball (finger hole side) and the bottom (solid side opposite finger holes).
b) Not more than one ounce difference between the sides to the right and left of the finger holes or between the sides in front and back of the finger holes.
2. For a ball weighing 8.0 pounds to 10.0 pounds:
a) Not more than two ounces difference between the top of the ball and the bottom.
b) Not more than 3/4 ounce difference between the sides to the right and left or between the front and back of the finger holes.
3. For a ball weighing less than 8.0 pounds:
a) Not more than 3/4 ounce difference between the top of the ball and the bottom.
b) Not more than 3/4 ounce difference between the sides to the right and left or between the front and back of the finger holes.
Altering a ball in any way, to increase its weight or cause it to be out of balance beyond the tolerances, is prohibited.
