Driveshaft 65 question!

Back in the late 60s my uncles made a haystack mover out of an old truck and it had the ball and trunnnion driveshaft behind a 413 with two transmissions. In low gear a snail could crawl away from it but it could easily move a big heavy haystack. One day they hit a rock with the driveshaft and it ripped apart right next to the rear yoke. They happened to have a driveshaft with regular u-joints from a International truck and a flange that was easily modified to adapt it so the stackmover updated to regular cross style u-joints with the splines in the shaft. It failed three front u-joints before my uncles got another ball & trunnion from a junk yard and had it shortened to fit. As far as I know it never had another u-joint / driveshaft issue until they started using the giant cube bails. That is what convinced me on the strength of the ball and trunnion!