Yea they are different unfortunately, if you upgrade to 29 spline you gotta get a new carrier, i have seen guys wheel those 27 spline shafts locked on 35s, id say get a different axle from the junkyard, it may end up cheaper (new 8.25 out of a late model xj). But if you do end up keeping this one, try to find like a track lock carrier in 29 spline if you can, rebuild it then use chromoly 29 spline shafts...