I cut a square, probably 8x8 out of the top of the muffler, then I removed the packing. Its a PITA because the packing around the perforated tubing is well attached.
Wear gloves because its messy.
Then I took a sawzall and cut the kidney shaped baffle out.
Be sure to take the time to clean out the muffler, I simply used soap and water then let it dry.
Then I had the top of the muffler welded back.
I hit it with matte black high temp spray paint and reinstalled the muffler.

I cant say just how much of a restriction the stock muffler is, it is baffled so thats a major source of the restriction, but I could say its not terribly bad for a stock muffler.