Gt383mag, I'm sorry, I was thinking SGT. You are correct, they are not splined.
...I suffer from CRS!
Here is why I think the drivelines don't last as long in a diesel as they do in a gasser. The engine with the front coupler installed and the input shaft on the pump are not aligned. If you look at the front rag joint connection you can see how they are off.
DSC03380.jpg
Another problem is that one of the bolt heads going to the adapter on the motor will hit one of the bolt heads that goes to the shaft flange as seen in the above pic. If you turn the motor by hand you can see at one point there is a nice gap between the bolt heads and then they will hit in the next 1/2 turn. I use cap screws now but you still need to grind them. I don't think Kubota knew what type of driveline CCC was going to use and you can see why in the pic below. The blue line is where the drive shaft flange is and it lines up with one of the bolts on the engine flange. The red line are the bolts that go through the rag joint.
DSC03398.jpg
If you do the driveline with the correct parts like it came with it should last a good 500 hours IMHO. That's pretty good and why I go back with the same setup. But I still think the CV is a better design.
Sam, I need to get with you on a CV type shaft. I don't know how large they are and there is not much room in that area. I have flexed my 882 enough that the drive line bolts hit the steering tube.