I took off the header, put in vice and used a 1" hole saw on a 12" extension. I did drill quite a few 1/4" holes as well. I started with a larger hole saw but found it was hard to position. the one inch on the extension worked very well. of course some long screw driver work was involved. on completion there was only marks left on the inside wall.
be prepared for the bit to bind, and don't breathe the dust.
The mechanic at the dealer I purchased my bike from told me that he uses a long rod to punch out the cat. He said that some is left in the corners.
Me I just cut it in half and cleaned it all out. It cost me $20 to have it welded back up.
Noooooooo! Dont do it. Cut the pipe and clean the cat out completely. You are asking for trouble that thing will leave all kinds of debris behind if you dont.
I figured if I'm going all the trouble to remove the headpipe, I want every damn bit of it gone. Wasn't that big of deal to cut the pipe in half, remove cat and weld it back up. Did mine for under $40 in one afternoon.