The 3.73 ratio is not listed in my chart. That wont matter much unless you are using stock diameter tires. 31 tall tires are going to match up pretty well with the 3.53 ratio gears. To get it perfect you can use a ratio adapter. The speedo gears are matched sets. If you mix and match speedo gears they are not going to mesh correctly. Your 448162 pencil gear doesn't show up in the chart I have. I don't know what drive gear part number mates with it. There were a lot of speedometer combinations and parts used during the later years. The change to plastic gears comes in around the late '60s. There were several part numbers. The key is to use the correct drive gear/driven gear mated combination. You should not use a combination that is not matched. As you showed in your photo, though you have a 15 tooth gear, it doesn't match your drive gear. I would say someone pulled a gear from a different vehicle like a Bronco or IH Scout. The pencil gears are made to match a specific drive gear.
You could swap in the original A-1511 and A-5707. These are for a 5.38 ratio. You would then correct the speedometer with an adapter from a speedometer shop. I would put together the best matched combination you can find and correct it with an adapter. This is the way most of them end up as getting the right gears is getting difficult. On mine I use the original gears and tall tire's and I "do the math" on the speedometer! I know how far off it is. I have seen the speedo drive gear slip on the shaft and cause a jumpy speedometer. This is usually the plastic gears slipping. Using unmatched gears usually ends up with an erratic speedometer and stripped gears.
Speedometer adapters: https://speedometercablesusa.com/gear_box_adapters.html
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Originally Posted by davide
