There is only one flapper on the 5.3 I had it cut out and covered the screen’s just right sound. Don’t know the part # on the muffler just know it was the 22”long one
All I did was use a trim tool pried up from bottom of mirror cap on front of mirror and pulled the cap off. Then just put new one back on .top edge first and snap into place
Stick your screws on the end of your t20 tool with hot melt Gun Gun then you can stick it up in the hole with out it falling off make it super easy to do