Scary steering shaft/coupler failure!

This is a picture of the steering coupler coming apart on my ’68 Barracuda AS I WAS DRIVING IT. The shaft is pulling back out of the coupler.Coupler coming out 1.jpg


In fact, the shoes had come almost completely out of the coupler right as I was turning back into the garage after a spirited tuning/testing drive on a mountain. It was horrifying. Anyway, I need help.

What I did leading up to this:
Newly rebuilt engine,
Brand new transmission
Rebuilt steering box from Firm Feel
Installed front sway bar

When removing the old steering box, I was shocked to find that there was NO roll pin in the coupler. Someone before me had been working on the steering at some point but I don’t know any more than that.

I loosened the nuts and bolt on the clamps on the steering column support and had my wife in the car holding on to the steering wheel as I pried/banged the coupler back off of the steering gear with a large screw driver. The coupler slid up the shaft no problem - it did not appear to be compressing the shaft.

Put in the new box and slid the coupler back on, master spline was lined up, roll pin went in. Thought I was done.

I understand that there are shear pins inside of the column. I have never worked on the column. Is a rebuild something I should take on or should I just seek out a new one? I’d prefer to keep more stock parts on the car if possible but this is truly a safety issue.
I have removed the steering column from the car and it is on my bench.