Some of the runners had anti lock breaks some didnt. Also some of them had leafs and others coils. The 4.88 diffs are offset inside which makes them Much more difficult to make other gears work. There is a way to do it but it takes grinding and weakens the 3rd.
As for the 5.71 gears......They are not what you would say weaker then other gears. What makes them more prone to failure is the speed of which they turn. Meaning to run a 5.71 on the street generates a LOT of heat. This tends to wear them out faster. They will stress the ring side pinion bearing. When setting up these gears imo its a must to use a master install kit and make sure the carrier is in great shape. Toyota carriers tend to wear out the carrier bearing sleeve making so the pinion bearing can be pulled off by hand vrs a press. Go read Zuks page and read about it there. He explains it better then I do.
http://www.gearinstalls.com/billyrear.htm
