You might get some ideas from this one. He made a limited slip differential out of bike freewheels in another video; however, I think he made a mistake with the brake because the wheels can still freewheel when the brake is on, and you can see that he didn't have a back brake when testing. You'd need wheels with individual disc brakes fitted to the hubs, then mounts for the calipers.I've been thinking about this and have realised that the reason tadpole trikes have the pedals stuck out in front is to bring the centre of gravity just aft of the front wheels. As you move the rider further aft then the effective wheelbase decreases and the machine becomes unstable. A four wheeler doesn't have this problem. This is probably obvious to everyone else but it wasn't to me! A four wheeler has the problem of needing a differential which isn't easy or cheap. So I was wondering .....why not make a 5 wheeler with the motive power provided by a 5 th wheel between the two rear wheels? The outer wheels would just be on stub axles fixed to the chassis. There was an extra powered wheel made at one time for push bikes, it was hung on one side and the engine was in the hub.