From the pictures looks to me like your pumpkin isn't centered you will more than likely need another size axle than what is in the other side. I know my truck has different size axles.
Have fun finding it too... chevy had a tendancy to change splines axle diameters and length every hop-stich. Some times the 2tons and 1.5 tons had the same axle some times they didn't. Lots of fun to try to find part... I know I'm still looking for mine at a reasonable price, try this link though. Through the parts manual I was able to find what years will work for my 47'
http://chevy.oldcarmanualproject.com/ However could also be the old axle broke near the splines and the end is stuck in the diff (This is what they tend to do if they break). If your lucky and have good balance you may be able to get a magnet on the end of along rod and put it down the axle tube and pull it out if not you may have to pull the diff...
Good luck...
Also had a question? Why does your truck have a transfer case is it a 4WD?
