I think if I had tried, it would have been easy to remove this C-clip through the fill hole in the front of the axle beam. I might omit it in favor of the valve-spring-in-the-slip-joint mod, OR I might try to create a snap ring like modern CV shafts use, but I haven't decided yet.
***UPDATE***
I've both picked the E-ring from a fully-assembled good diff, and created 2 snap rings that work, so it CAN be done.