Axle shafts won't go in the last 4"

[Robin]

I changed the front and rear axles on my 72 (it has a 69 frame and had drums all around). I had the spring perches moved (new axles are 1977) on the rear and it's all going back together nicely with new brakes etc. So now I can't get the axle shafts to go in the last 4 inches. I took the inspection cover off but I have no clue.
This is probably a simple fix, but I tried a search here and found nothing.
Any help would be greatly appreciated.