OK cool, I thought there was so much droop it was binding the U-joints. That would have been more difficult.
I had Inland Empire build a rear drive shaft with a 10" slip and a double 1310 Carden. It was spendy, but really gives a lot of leeway.
If I remember right it was about $350 delivered. I use a good grease with 15% moly to keep the splines slippery under load.
If there is a local welding school, might see if they want a "project" to weld up that old case for a spare.
And in any case, the more I look at all the work you've done, the more impressive your rig is. Great work! :beer: