I don't know of any that actually have mechanical linkages. The whole point is to use the alternator + electric motors as a CVT basically. You want the engine

I don't know of any that actually have mechanical linkages. The whole point is to use the alternator + electric motors as a CVT basically. You want the engine to be able to use it's maximum power at any given speed. The amount of gears you'd need for a mechanical transmission for the big freight locomotives would be absurd.