The rear shaft was made by a local truck/drive line shop. It was made using heavy duty tubing, not sure of thickness tho but it held up real well on my truck and is still perfectly straight and balanced. And yes the 1350 u joints are for a 14bolt.
The square shaft is homemade. Its a beast, couldnt break it if you tried. Its defiantly not balanced for running down the highway at 60mph. You could always add fluid to try and balance it. But it was never a issue for me, I just unlocked the hubs when on the street.