[Ant]

My understanding is the IRS axle side bearings and seals are the same for both 28 and 31spline, the axle bearing area diameter is larger than the spline OD.

All IRS housings will accept 31 spline axles if the carrier (True Trac/LSD) side gears are 31 spline. When buying the new True Trac carrier make sure the 31 spline side gears have the relief for the retaining clips.

When I purchased my Eaton Carbon Posi, the differential coy machined off the whole diameter on the inside of the side gear and clip wasn't encapsulated as it should be, they supplied new gears and I had the machining done. I purchased 28 spline axles from the Driveshaft Shop with 300m main axles and Chromoly Porsche style 108mm 28 spline CV's, I am not drag racing so they should hold up for road racing.