8.25 Dakota Gear Swap Wont Fit.

Over a year ago I bought a 27 spline 8.25 suregrip with 3.55 gears off a guy on ebay. I have looked up the number on the gear 2852943-3.55 which seems to be correct for a dakota and should fit my 8.25 housing as he described. I have a 74 dart sport that had open 2.71 gears. No question I have an 8.25 rear. The races and bearings are bigger in the newer one and the carrier is just too damn big. Not by much, but it hits. What is going on? Anybody have an idea?