Rex and Freud - excellent advice all around. I may make 2 sleeves - one for mockup to determine the exact "best" overall length. This sleeve would be slightly oversized to allow a telescopic-type adjustment.
The second, and permananent sleeve, would be a shrink-fit as described above.
I am very fortunate to work in a facility with qualified machinists and some heat treatment capabilities. This will be work for our CNC guy. I can do rough cuts on our manual lathe, but the ability of that lathe to hold tolerance, and my ability to operate it effectively, are far from ideal.
What do you guys think about pinning the sleeve to the shafts in addition to the shrink and weld? In my own mind, I have gone back and forth on that topic.
Steve.