I've done a bunch back when I owned a 57 Chevy car back in high school. They would last just about a month. But that was 40 yrs ago!
But Seems like I remember snap ring inside the extension housing you had to expand to get it loose from the rear mainshaft brg.
Oh my son did a couple also, they didn't last any longer for him in his '64 pickup than they did for me in my car. I have a 1962 motors manual down in the shop though if you need particulars from it just ask!