If you take a 15.3 Brunswick Karma with 2-3 top and a 3.5 inch pin and simply drill the fingers through the Cg without a thumb hole, is this a legally drilled ball?

If you take a 15.3 Brunswick Karma with 2-3 top and a 3.5 inch pin and simply drill the fingers through the Cg without a thumb hole, is this a legally drilled ball?

Yes as long as the ball meets the static weight requirements.

If throwing a ball with no thumb, the fingers are your center grip line for measuring static weights. If the cg is located near the fingers (and no thumb hole/weight hole is added) it will never have any issues on statics unless the ball had 4.5ozs plus of top weight.

Most bowling balls drilled with two fingers and a thumb with no additional weight hole meet the usbc guidelines for use by no thumb bowlers when weighed on a scale based off the finger holes being the center gripline.  If you get board just check random equipment you may be surprised.

CG's are mis-marked all the time.

You have to balance the ball to be sure.