There are many different pinion gears. They can range from 8-12 teeth. It depends on the gear ratio of the set (ring and pinion.) GM installed several ratios in production cars so one cannot make a blanket statement. It would lead you in the wrong direction.
The gears are the same for posi and non-posi.
From a Richmond catalog here's the ratios for 8.2"
Teeth Ring-Pinion Ratio
25 spline pinion
27 spline pinion
You will need to determine which housing you have. The cover gasket is the key.
If the gasket is 11" oval with 10 holes it's a 25 spline.
If the gasket is 10 5/8" irregular shaped (two scallops at 9 and 3 o'clock) it's a 25 spline.
If the gasket is 11 1/2" irregular shape it is 27 spline.
I bet it's likely a 25 spline.
I-man has an error in his post, 37/9 = 4.11
Gears are matched sets. Mixing and matching pinions and ring gears is a no-no and may lead to problems such as noise and premature wear. That's also why people could not tell you what your gear ratio is. If you have matched sets, but are missing the pinion, you cannot determine what the ratio or pinion should be. If you are lucky the ratio is etched on the ring gear.
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