Yeah I was definitely planning on making my holes bigger than one inch.  I'm glad you tried it first 

 It's too bad a 90 degree drill wouldn't fit into the inlet pipe.  That way you wouldn't have to cut into the muffler shell at all.  Although it may be possible to fit a sharpened bar with a 90 into the pipe.  Then you could wack it with a hammer.  HMMMM