Changing L6-30 to L14-30 question

I have an old mobile generator mounted on a frame with tires and a hitch. We pull it with a vehicle. It has the neutral bonded to the frame. It also has a ground lug on the frame and we use a rod.
The output is an L6-30 3wire. Can I change it to an L14-30 4wire and how do I handle the grounds & neutral if I do?