The biggest area of concern with drillings is static weights.  This link covers it well.

http://www.jayhawkbowling.com/Pro_s_Corner/Balancing___Weig/balance.html

Other than that look at Chapter VI in the ABC book. Especially to see that you can only have 5 fingerholes, one weighthole that is 1 1/4" in diameter or smaller (including bevel, chips, etc.), one vent hole of each finger that is in diameter 1/4" or smaller, and a mill hole that is 5/8" in diameter and 1/8" deep or smaller.

https://www.bowlingmembership.com/PDF/03-04PlayingRules_workingcopy.pdf

For extreme details, look to Chapter III of the ABC Equipment Specs manual.

http://www.bowl.com/bin/pdf/specsmanualaug2003.pdf

Finally, the ball must be approved by the ABC.  Here's a list...

http://www.bowl.com/bin/pdf/approved_balllist.pdf

Also here's some more recent non-conforming balls...

http://www.bowl.com/bowl/BowlDotCom/common/static.html?page=bowl_speccert_balllist_nonconforming
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Good luck & good bowling