To install an aftermarket steering U joint, you are likely going to have o cut your original shaft. All of the aftermarket joints I've seen connect to the steering box and then directly to a female round, splined, or double "D" shaft and you can't get to any of those choices with a bare shaft end on original Mopar steering that I remember without cutting the shaft.
Now, to be honest, I haven't looked at the steering u joint options for a few years, maybe someone makes something now.
Just glanced around
www.borgeson.com they have a joint for 62-82 Mopar cars with a vibration dampener, says you have to cut your steering shaft.