I think a lot of the reason it broke is your geometry on the makeup.
A single rag joint and u joint way down at the end of the shaft allows a lot of leverage on the long stub. Mine is done differently and I'm less worried about it. No less "rigged" than yours -- but I think the configuration puts a lot less stress on the point where the steering shaft joins the steering wheel shaft.
Depending on the angle of your steering box and so forth, a single u-joint with a rag joint may just have caused to bending stress on the shaft which concentrated at the join.
My u-joint at the box is more of a CV type that has the sliding piece inside it. It's pretty flexible and can telescope at the same time. You can't see that joint in the pic above. But you can see the Chevy AstroVan u-joint and the 3/4" solid rod.
The piece from my original shaft is press fit into the AstroVan u-joint which had a 1" DD end on it. Then I welded it to the joint.
So far so good. We'll see if mine breaks.