No. The switch over was above 4.10. 4.10 still used standard carrier. 4.56 needed the spacer or different carrier.
Could be true, but for all we know the 4.10 gears that are in it NOW were not the driving factor for the lack of BOM numbers on the axle from 50 years ago. The statement from the service manual is still a possible explanation for the lack of BOM numbers on this axle.
