FWIW......I always ran with the stock ball diff in the rear and up front I replaced the balls in the stock diff with the Tamiya Hop-Up Options 3x3mm Bushings for Ball Differential (12pcs) part number 54424. These tiny plastic bushings allow you to lock down the front diff to make a spool, or adjusted for a limited slip diff. Less expensive than buying the full option solid front spool.
Spec-R also sell a gear diff for the TA-05 but I have no experience with these or the ones from 3Racing.