Jeff'z, Glad you found the problem, the 'Okie Bushing' as it's called can be found at most old truck vendors like Jim Carter's or Chevs of the 40s, both have web sites. This bushing goes in after you take the 'U' joint appart, just drives in between propeller shaft and tube and you're done. While your at it, you might want to inspect the diff inards while the cover is off, just look for broken teeth, rotten bearings etc, also feel around the bottom of the housing for metal chunks. If all looks good you just need to re-assemble the thing per the MANUAL.
Best of luck
