Here is the chamber wall removed with the first 1 3/4 inch hole cut.

I hade all the holes covered with a piece of steel to give me a solid chamber wall and a good surface to drill the two holes for the new pipes. You can see the weld lines of this piece in the picture here.

Here is chamber wall drilled and ready to go back into the main housing. I inserted the chamber wall in the housing and put the pipes in and alligned them by eye to find the center for the holes. Basically you want to make sure they come straight out the back of the muffler housing.