When I replace axles, I measure HUB face too Hub Face.    I tell the seller what axle weight size and also buy new U-Bolts to match as well.   And where possible, I "up size +1 as well.   re:  If warped or broken axle is 3500 lbs axle, I ask for 3800 lbs axle and I "up size" +1 its new leaf spring packs as well.    When I get the axle and springs, I then measure my leaf spring saddles location myself and get my local welder guy to weld them on.   When replacing axles, don't over think it.  Just +1 up size and mount the leaf spring saddles yourself.    It's that easy...