M40 4 speeds came with 4.10 axle. M41 OD box with 4.56 axle. Wagons used M40 with 4.56 axle. Factory spec Wagons never had OD but many have been retro fitted. If you had a friendly dealer you might have been able to have the OD fitted to your car/wagon at the time of delivery but that would have been expensive as you would have an M40 gearbox left over. The 4.30 axle didn't arrive until the last of the B20 models and most people won't actually know they have one. They seem to have been fitted rather randomly to the cars. It's a good ratio to use with an OD nowdays. 4.10 good for economical cruising but takes the edge off performance unless you've upgraded the engine.