A-833 speedometer cable Swap

I also would like to know what speedometer gear I would need to put in it. The A-833 I bought is from a 65 Coronet (I know it's from a B body, but I only have to make a bracket to relocate the shifter). So how do you calculate what tooth gear you need? does it depend on the size tires you put on or the gear ratio in the rear end, or the combination of both? The car was originally an automatic I'm converting to a 4 speed. Can I use the gear in the original automatic in the A-833? Just so many thing I don't know, It's confusing. :(:thankyou: