Mopar 8.75 posi. wont work. Why are there 2 rows of spline?

Sooo I should have the rear dif. rebuilt. Did someone mention that I can fix my problems in the center section? Darter 6 you said "He has the rebuild parts to up grade what you have.Just to let you know the Eaton set up with green bearings was raced alot before the change over so the axles did fine with the single spline set up." Do you mean I can just have single splines put into my posi and put it in and go without having to deal with getting new axles or shortening the housing?