How can I tell if these are HiPo Axles?

[gt350hr]

     Because a 28 spline carrier is "bored" to accept the smaller 28 spline axle on the ends where the bearings press on. "Internally" the carriers are all machined the same. The "hub dimension is the same on 28 and 31 spline side gears so they will interchange. To further complicate this the 28 spline carriers can be machined for two different ID carrier bearings. 31 spline carriers are all machined to the larger diameter and must use the "slim line" bearing if used in a "small bearing case".
     Randy

[mygt350]

Randy
Have seen the different part numbers associated with the different carrier bearings and did not fully understand why they were different. So although internally, the 28 and 31 spline carriers are the same, the outer bearing on a 31 spline carrier has larger dimension which would require smaller (slim line) bearing for use in a 28 spline case. Normal outer bearing if used in a 31 spline carrier, slim line used in 28 spline carrier.

[gt350hr]

    A "small bearing" is # 501349 /501310 . This is small ID and OD and what was original on 65-66 Mustangs/GT350s as they used the common single rib small bearing cases ( C4AW -A) with a 2.891 housing bore. The large bearing is #603049/603011 and fits the "nodular" C4AW-B case commonly called "3.062" for it's housing bore diameter and there were some single rib cases as well. To allow a big bearing carrier to be used in a small bearing case the "slim line" bearing #102949/102910 must be used. I have to stock all three because I never know what I will have show up to be rebuilt!
  Randy

[pbf777]

................ the outer bearing on a 31 spline carrier has larger dimension which would require smaller (slim line) bearing for use in a 28 spline case. Normal outer bearing if used in a 31 spline carrier, slim line used in 28 spline carrier.

    Not exactly.  As I recall, the earlier ('57 thru say '65 +/-) 9-inch carriers used a smaller I.D. bearing of 1.625" with an O.D. race of 2.891"; which I presume proved to provide insufficient material thickness of the bearing snouts to support the increased power as time passed and particularly with the larger bore I.D.'s for the 31-spline applications, so then 1.781" I.D. was adopted ('64 or so thru the end of production) for either the 28- or 31-spline fitments with a 3.062" O.D. this also often referred to as the "Big-Bearing", but then later ('69 +/- thru the end of production) the 2.891" O.D. returned, this leading to the so-called "slim-line" bearing, but more frequently referred as the (later) "Small-Bearing", as used with either the 28- or 31-spline axles.   

    Or something like that!     

    Scott.

    P.S. Since Randy beat me to it while I was hen-pecking I'm just adding some more B.S.     

[gt350hr]

    Great minds think alike . LMAO