I'm not positive but since they offer the extra-strong axles with new hubs, I believe the hubs will fit the existing spindles and bearings with no boring required. I'm sure they just machine the inside of the hubs out and then machine new splines so that the inner diameter is larger and the splines count is optimal. That will probably make the hubs a bit thinner but I assume that's not an issue nor where the weakest point is.