Most 350 duellys are a dana 80 the 450 is a dana 110 If I remember correctly. My 2002 f 250 superduty had a dana 50 front and a sterling 10.25 rear my current 2006 f 350 has a dana 60 front and sterling 10.50 rear. I beleave all superdutys have a dana 60 front after 2004 but the rears are still mached the same. But as I said there could still be some oddballs out there.Just cheak the axl tags.