I counted the pot metal gear (the one behind the brass gear) on the 83 and 85. they both have 20 teeth.
The white gear on mine looks just like yours when I line it up as you have your`s set. 9 teeth, and the other end has 15 teeth.
There is one more worm gear deeper inside that drives the one that drives the brass gear. I don`t know if that one is the same in all spedo`s.
when you are at a PNP grab some instrument clusters when you see them, usually I see them ripped apart for what ever reason with the face and needles bent. why people destroy them is beyond me. one of my 85`s was all bent up, but I wanted it for parts for mine if it decides to crap out. can`t have too many parts.
I think a whole cluster is $35.00.
Charlie