There are closed knuckle Dana axles and there are Toyota Birdfield axles. Two different things.

I have a Detroit locker in my stock rear axle. I have pulled my front axles apart and put in new grease. Other than that, my axles are 1967 stock. I have driven my truck through some pretty crazy obstacles at off road parks in Texas, Tennessee and other places.

Yes, anything can break. But I have had my truck standing on the trailer hitch while I was hammer down on the 396 with the big XZL tires hoping and bouncing all over the place and the truck just sitting at the bottom of a dry water fall.

Same basic thing by a bunch of us in the Texas Hill Country back in 2007. Multiple stock trucks climbing rock stair step ledges.

Pretty much if you don't go full lock with the steering and floor it in low range 1st gear. You have to work hard to break the stock axles. Yes, open knuckle axles have larger diameter shafts inside. But, a stock truck doesn't really have that much power either.

I also like disc brakes. I would suggest you plan to take each wheel cylinder apart, clean, lube and adjust. Even if they work now. If the truck has been sitting for a few months there is probably at least one seized wheel cylinder piston. A properly functioning M715 brake system is really very good. I have swapped to a dual line master cylinder with power brakes. It will lock up all the tires with a toe twitch.