I have seen some rebuild kits for E85/E86 rear differential bearings which use two rows of ball bearings instead of the standard taper bearings (see image below). I am not sure what the reason behind using ball bearings instead of taper bearings and personally when I come to do my differential bearings I will be using taper bearings, but only because this is the stock/default bearing type.
My dad was surprised to see ball bearings. He’s a mechanic so he has done a rear diff or two My guess was that someone rebuilt it using an older rebuild kit or used whatever they had laying around that fit.