There's only one safe way to shorten a steering column, and it involves machining both ends of the cutoff shaft for a "Double D" coupling that's available from various racing parts suppliers.
Jerry
I had a machinist cut the lower 2” of my shortened original shaft to a DD shape, used a U-joint with two through bolts, and improved the safety with a telescoping DD connection to the steering box. That is the ONLY way I’d recommend doing this. The slip on “round” lower shaft pieces that are welded to the original shaft have the risks you mentioned.
HERE ARE THE DETAILS of what I did to mine but it doesn’t show the steering column shaft end very well. It has a DD end with a through bolt for the U-joint.
