Are you investigating bearings because you have diagnosed a problem or are you just seeking a project?
how many miles are on your car and how many miles do you put on your car each year?
Many rear axle problems are a result of excessive wear on the stub axle’s. The miles on your car and/or known upgrades or maintenance would provide a clue if the bearings have in fact reached the end of their life span
The stock OEM bearings are readily available and the process does require some skills and a hydraulic press, but it is not a difficult or precision task.
I know of nothing inherently inadequate with the stock bearings, certainly no more so than in any other classic automobile.
Sometimes original is good enough.
Larry