Re: eb were are the weak points
Compared to any other 4x4, out of the factory, there are no weak points. My brother and myself both own old broncos, and until lately have been completely stock with the exception of 4" lift and 33" tires. My brother's bronco had the D-30 front which NEVER had problems. The Dana 44 is superior to the 30, but only if you do lots of huge rock crawls with huge tires.
If huge tires are what you are looking for, then definantly a D-44 and 31 spline axles. The stock steering box (power and manual) have a very long sector shaft that is known to fail with very large tires. There are several different mods that will work to place a different box with a shorter sector shaft.
The stock tranny in some cases is garbage (RAN vs RAT) not sure which stamp is which, but one of the two is terrible. You will need discs for sure. All other parts should hold up to the abuse.