Third Rail SD 7 or 9 a few years ago. Click on the link. Note that the wheel flanges are small, IMO. This design is not a two vertical can drive. A horizontal motor with belt drive to the fuel tank and drive shafts, to the front and rear truck. O72 limit may be related to this drive shaft arrangement, there is a limit to the drive shaft bend, IMO. ???If Third Rail uses the SD model design for the GP model???.