Right rear halfshaft play: outer CV?

[Russ Maki]

OK, so I got to playing a little rough at the local ice time trials Sunday
with my '87 4000q, grooving on how I could power oversteer through turns on
lake ice with the rear differential locked.

Yesterday, I started hearing that telltale "chunk, chunk, chunk" at low
speeds, increasing in volume as I steered left. I got under the car this
morning and discovered that the right rear halfshaft has some play in it
when applying force parallel to the shaft.

It looks like the shaft is moving in and out maybe 1/8 inch at the outer CV
boot. At the inner joint, the movement is at the flange rather than the
joint.

I'm assuming (hoping) the failure is the outer CV rather than something in
the diff. I figured if I broke something in the differential it would be on
the left side, where all the locking goodies are.

I do have an '84 4000 parts car with what appear to be sound halfshafts; can
I use them on an '87? Also, it would probably make sense to install a used
left-side half shaft as a replacement on the right side to reverse the wear
pattern, no?

Thanks in advance for the insights -- I know there's a lot of knowledge out
there on this issue.

Russ Maki
Ixonia, Wis.