Mixture Screw is Stuck

Hi there.

I have the stock Keihin carbs on my parts bike (81 KZ750 E2). I want to clean then up, but I can't get two of the air/fuel mixture screws out. The last person who tried destroyed the top of the screws, so there is nothing to grab onto with the screw driver.

Any recommended ways to remove these mixture screws? Is drilling them out the only way?

Thanks.

Never mind. I found some information in another thread.