This one ends well.
If you remember:
[I started with the Odometer working but not the Speedo.
Got an '87 instrument Cluster, but the Odometer did not work because the little white gear was damaged.
The goal was to keep my '89 Odometer with 214,000 miles.
I managed to pull the '89 Speedo apart and discovered that there
was a short across the 2 terminals connected to the needle coil.
Removed the needle, face, and coil section and removed 2 boards,
one of which (I believe) is for the Service Reminder,

Now, the $20,000 question... The '87 Speedo only has the single
board containing the Odometer gear. Can I install the '87 board
on my '89 Speedo without a problem, I don't really care about the
Service Reminder.]

Although I got no reponses, I went ahead with the conversion,
and lo and behold...both Odometer and Speedo work now.
One minor hangup is that the Speedo now reads about 5 mph too high.
At some point I'll re-calibrate the needle by rotating it back.
(Thanks KarmaticLove for the good advise).

--
-Cool Volvo- 1982 240 4 Spd OD w/ 227K, 1989 240 5 Spd w/ 214K. Used to own 1966 122, 1968 144, 1970 145, 1972 144, 1980 245