I don`t know the exact diameter of the stock headers,but the 1-1/2"x 12" J&P baffles that I put in them [after cutting off the kink,of course] are a tight,rattle free fit.They were too loud and raspy for my old ears,so I made a 2 into 1 pipe,

and used a piece of a Thrux can and a piece of stock Bonnie can,and got a deep rich sound,even though the can is hollow.

:-D All thats left is a short support strut and a bit of header wrap on the non-shiney bits. Steve