I once put the 65 Dart GT into reverse while in fast idle, and the driveshaft blew apart like a paper towel tube.
It was rusty.
But that's when I learned about the ball and trunnion front end.
Made do a while with 66 shaft and conversion ujoint plate.
Finally went to later 904.
My 66 383 has a huge inertia ring at the front end of the shaft to dampen vibrations....anyone else have a big fat flange at the front end of the driveshaft?