It states that both are 2.5" offest inlet and 2.5" center outlet. The only difference I can see is that the 12256 is a 5"x8" oval muffler while the 11266 is 4"x9" oval muffler is there a big difference between the 2 or they about the same? Im fixing to order one or the other.

 

I used the 11266 and it works fine. I did have to add a length of pipe to make up the difference in muffler length between the factory and the new one. I sounds nice, not real loud, but you know it is not stock.