John,
There are 3 speedometer driven gears currently available for the Muncie 3 speed or 3 speed OD transmissions: White 25 teeth, Yellow 24 teeth, and Green 22 Teeth. The drive gear does not have to be replaced to use either of them. I get the gears on ebay from Muttonhollow Chevy. He usually has the best prices.
Changing the gear oil is a good place to start but any grinding in 2-3 generally indicates a syncro problem. Don't rule out the clutch though.
Fred
Note: Earlier regular 3 speeds used a 19 tooth steel gear. They also use a different drive gear.
Also, the SM319 is a factory overdrive and would make a serious improvement in overall driving and also lower engine rpm's.
