On my J3 I am changing my A65 to a C85. I understand a modification has to be made to the current A65 muffler by the way of putting a "dent" in it. Is that proper and what is the "dent" for? Does it require a mod entry? Also, I understand there may have to be a modification made to the exhaust pipe. What would that be? Any thing else I should know so as to stay away from any unwanted surprise?