Stumped on rear axle..Please help

[csfields]

I never paid attention during tear down and only caught the problem when going back together and had issues with installing new wheel cylinders, one obviously went in easily and the other I had to remove the bleeder screw to get it behind the axle flange and onto the backing plate, due to it being tight. I am sure it's internal, just not why. The axel tubes are the same length from the pumpkin, the backing plates are the same, the axles are the same. Everything worked fine when driven. Obviously, by the wear pattern it worked for some time. I'm just coming up roughly a half inch off when measuring from the center of where the pin would go, to the edge of the axle seal. I googled the casting number and it shows it was a 12 bolt truck rear end. Of course can't believe everything you find on the internet.