[wilkin250r]

Warning: Gears are NOT simple. They look simple, because it's only a few components, but they are actually very difficult to set up. They need to be very very precise, often putting in shims that are thinner than a piece of paper, and require specialized measurement devices to check clearances.

I don't want to be the jerk, but the simple fact that you're asking questions about ratios tells me that you're not ready to rebuild this differential yourself.