Thank you edb.
My guess was that it enabled, or was an attempt at enabling some sort of repair while shortcutting something complicated or time consuming in the process.
It is interesting that it may have actually been recommended by Cat. I think there is still enough viable spline to run my cable control, but I intend to limit the ability of the coupler to float to a minimum. I can screw a bolt into the spline on the CCU and secure it with Loctite. (There is a threaded hole in the end of the shaft. I think this will keep at least an inch of engagement, maybe a tad more, and not create any tension between the upper shaft and the CCU drive.

The wheel tractor is handy, but mostly due to its portability. I know of nothing that takes the place of tracks!

H AA,
it goes without saying that that oxy. cut was somewhat extreme--the Cat machined cutaway section is much less than that--I did find that the cutaway is shown in my only D6 U Parts Book (9U13263-up)--albeit ever so small.
Nice wheel tractor with useful blade.
Cheers,
Eddie B.