Doug, Here's the procedure for selecting the correct speedo gear part number and tooth count. Start with the chart that says which transmission you have, 3-speed or 4 speed. Then go to your year and model, Tire size, axle gear ratio (ring and pinion tooth count), then the speedo gear part number, then to the chart of part numbers to find the tooth count of the speedo gears. Unfortunately, in the example I picked, they have an error, as the same speedo gears can't be used for different axle ratios. But that gives you the procedure.
The 1927-1957 Parts book
LINK has more believable data. The same procedure will apply. Go to the pages after the one I linked to find the listing by 3 or 4 speed transmission.
[on edit] I didn't go back and see if you had a 3 speed or 4 speed.
Anyway, I tried to see which one the 1929-1957 parts book would say you needed, but that was a bit strange as well. It comes up with a 7-20 speedo gear set. So if that's what it had and someone put a 13 tooth driven gear in it, I'm sure it wouldn't last long as it wouldn't mesh well with a 20 tooth drive gear.
You could just go by your axle ratio, assuming you could find it in the charts and then go to the tooth count on the speedo gears. The tire size would make a difference, but unless you have radically different tire rolling diameter, it won't be a large change.
