If you're going to be spending the same amount of money either way, go for the 31-spline axles. They won't have the same bearing as the big bearing 31-spline axles, but they will be a stronger axle. Be warned, though, that they aren't designed for larger tires. In talking with the guys at Currie, they know of about a half-dozen small bearing axles that have failed when combined with 33" and 35" tires. The bearing pulled right off the axle. They consider this an abuse issue and won't warranty the axles. If at all possible, I'd recommend waitng on the rear end build. Otherwise you'll end up doing everything twice--eventually. Take it from me, I had a SB with 4.11 gears and a Detroit and I was always trying to keep that thing alive. Now many dollars later, I have a BB with 31-spline axles, an ARB and disk brakes. Hopefully I'll never be replacing that thing!