MBRP.....

I was going to order an MBRP turbo back exhaust for my 05 F550. They place where I'm getting it said it wouldn't fit because of the bigger rear axle in the 550, is this true? If so is there a way around it. like ordering a different rear pipe from MBRP? If not can someone recomend another good exhaust system for the F550.
I am new to the diesels and don't really know the best stuff to put on. Thanks.