I found some Magnaflow's at itpdiesel.com and they show 4 different sizes for the diesel muffler. Diameter is all 7" but the body size choices are 14", 20", 24" and 30". Overall length is 20", 27", 30" and 36". The one I saw posted here was part number 12772. Aluminized was $105 and SS was $130. Not much difference. Does the size of the body have any effect other than tone? Want to put a new muffler on soon so I appreciate any advice.