rich-
without knowing what year exactly dana carrier you are taking about, I urge caution. From what I have learned over the years, there are many varieties of dana 80's. even the cases are different for the numerically lower ratios. the 80's in our F450's are the toughest out of the batch. good is that they don't break. bad is there is almost no hi-po goodies for them. I paid a fortune for a complete built 4.56 years ago and love the extra top end I get from it. Never really thought about a posi since my carrier does not like soft surfaces whatsoever. Quite frankly, the front end sinks into anything mushy and the rear just spins on top of the stuff.
Off the beaten track...I know there is a way to decipher furd p/n's to year, car/truck, etc. the info is in there, I just don't remember how to decipher it.
I will check with a buddy of mime on monday, he works at a local stealership parts counter and he is the one who taught me years ago on the p/n secrets.