Just wondering since a powertrax lockright #1810 fits both the 8" and 9" rears, and both 28 and 31 splined axles, does a 9" 31 spline side spider gear fit in an 8" case? I have heard the 28 spline axles are the same in same width 8" and 9"ers. Sooo, why cant a 31 spline fit in the 8"? Thanks.