speedo cable gear

[123abc]

can anyone calculate the speedo cable drive gear needed for this application
1970 mustang
fmx box factory
8 tooth gearbox drive gear with 3.25 rear gears lsd 9"
rear tyres are 255x60x15 and are about 680 mm in diam

[hybrid]

We have a calculator in the automotive calculators section:

https://www.mustangtech.com.au/Calculators.html