Odometer problem
 

Hello,

This is my very first post. I have searched all over the internet to find a solution for my problem, but unfortunately I couldn't find anyone with the same problem.
I hope someone can help me with this:

I have a Porsche 911 SC with a MPH speedometer. I want to change it into a KPH speedometer. I already have changed the dial. Also I have ordered the conversion gearset for MPH to KPH. After the change the odometer hoewever counts slower than in miles (now it counts half a kilometer when I drive 2 km).
The first gear in the speedometer should be a 20x30 gears. However mine has a 20x36 gears. When I look at the internet this gear shouldn't even exist...

Can anyone here help me with the right gears for this speedometer?

these guys can help you out...
https://www.nhspeedometer.com/