If the tooth count is the same, and it appears to be from the pictures, and the pitch is the same, then you can probably make the rest fit with some turning on a lathe as long as the internal diameter is not already larger. Then it would get a bit tricky making a sleeve. Have you checked against other Rover products? The Rancher Autodrive ride ons have a couple of similar sprockets in the final drive, perhaps something there will fit?
