Axle splines depend on your carrier not ring and pinion. I have these gears installed in an otherwise stock 28 spline differential. Also highly recommend getting the FMS traction lok clutch rebuild pack and do it at the same time!
I do believe the gears themselves don't dictate what spline axles you use. A gear swap doesn't interfere with what spline axles you use. Please confirm this with a tech here but when I installed mine, what spline axles I had was not required.