You are rebuilding the differential in your muscle car and you want to calculate the gear ratio. This can be done quite easily. Carefully count the number of teeth on the small gear (SG) and write that number down. Then carefully count the number of teeth on the larger gear (LG) and write it down. Then, you can perform the following calculation: SG/LG equals gear ratio. If you need to know what gear ratio to use in your custom built differential, there are websites you can visit that will perform that calculation for you.
For more info, see The Pros and Cons of Installing 4.10 Gears