10 and 12 bolt 'rearends' both have 26 spline sidegears. However, I believe the sidegears not to be interchangeable due to a series of technical opportunities I had while trying to figure out what was wrong with my rear locker I discovered that the 10 bolt bearing race for the sidegear is larger. So, when I went to put in a 'regular' locker it had slop in it which caused many broken parts and bad driving characteristics. I'm now running 12 bolt rear with Samurai LockRite, and Samurai sidegears which must have the casting flash ground off of the face in order to fit proper. A Sidekick LockRite that uses Sidekick Sidegears would be just fine too...
-Eric