I dont know nothing about actually plugging, but I do know that clay works very well. It is reusable and better at sealing; most notably with older columbia balls that have engraved logos. The plug tends to seap through the foam dams. Super cheap to buy too.

at the proshop i help out at, we use a two part epoxy from ebonite.  The pumps are pre-gauged so its a 1:1 pump ratio.

Make sure you drill out any bevels made from the previous drill and make sure those edges are square or you'll have chipping.  You don't have to rough up the surface of the hole coz the epoxy is made out of the same stuff as the ball.

Things to note:
1) Make sure you get a good mix from the 2 part epoxy (mix 5-10mins)
2) Fill the holes half way at a time to ensure proper and consistent hardening
3) Drill out bevels to aviod chipping

To knock down the excess, there's a special "blade" that goes on your drill.  I have no idea what its called, but it's curved to the shape of your ball.  Just make sure your pitches are all zeroed out or you'll hurt your ball.  Hope this helps.
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Bowling Since March 2006 - "Get coaching, don't worry about it"...blah blah balh...Just answer the questions please

Thanks for the info guys. The link to the Jayhawk site was excellent. Been to that site before but somehow missed all that info. Good tip on the plumbers putty also. I'm looking at ordering some materials from the Innovative Bowling site but am going to do it over the phone. Their item descriptions leave alot to be desired and I got some questions. I'll probably go with the 1 gal kit for about 68 dollars. Can't wait to start trying some different drillings for my thumb. My thumb doesn't get sore at all but it always feels like I have to squeeze too hard to hang on to the ball. Could be me or not. I'm figuring on trying things in 1/16 increments since I don't want to hurt my hand.
 
Thanks
Dick