Does anyone know what the difference is between the JKBVNKA1-4A010963 muffler and the JKBVNKA1-4A010964 muffler? It appears the ...963 was used on the 2003 models and in 2004 they used the ...963 and the ...964 mufflers. I'm trying to convert back to stock mufflers and have a new one I got off of Ebay that came off a new 07 1600 Classic. The ...964 mufflers appear to be the ones used from sometime in 2004 through the current models. I wouldn't think the bikes frame has changed, especially during mid year 2004 when both models were used. The Kaw on-line diags show different part numbers for the "complete muffler system" but the visuals make the welded brackets look the same.