I'm going to put a different muffler on my 12v to quiten down my stacks, especially when towing. I decided a Donaldson's the way to go but I also read on another site about a 40" nelson. Is this the same as a 40" donaldson or are they different. Either way I'm needing the part # for the 40" and the best place to buy. I need the 5" inlet and outlet. Thanks in advance.