The 489 obsession

The 741 has a larger pinion stem than a 9" Ford. However, the Fjord has three pinion bearings, the third one solely to support the head of the pinion, which gives it a lot of strength (the pinion head is loaded in shear by the ring gear). If you're going to break a 741, it will probably be right at the pinion head, the area of greatest stress.
The other two cases have a much-larger pinion stem at the rear, the 489 being 1-7/8" and the 742 being 1-3/4" if I'm remembering correctly. That means you've got a lot more support at the most critical spot on the pinion. However, both are 1-3/8" at the front bearing, same as the 741. When the bigger pinions break, they usually shear just behind the yoke or the front bearing. Also, the 489 can suck the pinion head into the diff if the crush-sleeve arrangement is retained. I've owned more than one diff scarred by such behavior, but I received them that way. I've used solid spacers for years.
Personally I've never broken any of 'em, but I've seen all three break, generally as I've described and almost always under extreme duress--slicks, trans brakes/clutch dumps, etc. I've also seen them endure enormous abuse--some at my own hand. Still, if you don't plan to beat the ever-livin' shyte out of your car, you'll probably never have an issue with any of 'em.
If you do expect to engage in such shenanigans, you might want to meet my friend Dana.