Golden Motor has kits for either or both wheels. I have found another company that does as well but did not bookmark their site apparently. I do live in a very rural area and am moving further out soon. At that point cycling will be out of the question. it takes 90+ minutes to drive it at 60 mph most of the way.
I know the motor will add some weight and I am not a lite guy. I was hoping for speeds at or near 35 but am not sure I could carry enough batteries to accommodate most of the trip.