+1 on having the existing rear end rebuilt. Once rebuilt, it will be as good as new.
I would recommend to NEVER install a salvage yard rear end in your ride without having it first re-built.
The cost of the re-build kit is around $125. The labor is several times more expensive.
It also may be possible that just certain bearings have gone bad. If for example the carrier bearing are bad, the cost to replace is much lower in terms of labor and parts.
Wheel bearings can be replaced by the home mechanic.
If the Pinion bearing is bad, recommend rebuilding the enire rear-end.
Have you performed an inspection of the internals? You may be suprised at what can be learned just by looking at the condition of the oil and gears. The center section is not all that hard to remove. Once removed, the carrier bearing can be inspected.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.