[HO455]

What are your plans for the truck?
I believe you can get the numbers off of the bearings and source them from a quality bearing house.
As far as the gear set goes it depends on your comfort level. If you are unable to source a ring and pinion you could acid wash the rusted areas to clean them and then reinstall them. After all this kind of rusting is common when vehicles are parked for extended periods of time in humid areas.
How many times do people start driving vehicles that have been parked long term and never crack the cover on their differentials? Yes the ring and pinion may fail after hundreds of miles of hard use or after after tens of thousands of miles of light use.
The question is can you live with a possible pending failure? The failure isn't likely to be sudden or catastrophic but a slow increase in noise and slop in the rear end.