The one you have out is the driven gear. A 13 tooth driven gear would be paired with either a 4 or 5 tooth drive gear on the transmission shaft. You probably should match what your drive gear has unless you've changed axle ratio or tire size. This page and the next in the parts manual may tell you what combination of drive and driven gear you have.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.