I've got a Goldwing 1800 w/Motor Trike. It just so happens I was in Las Vegas over the weekend and rented a Champion Goldwing trike from Eagle Riders. They also had a Harley Champion trike. I was talking to the owner, who did the conversions, about the two. He commented that they both handled the same but that the Harley was "severely under powered". He said they had tried different gear ratios to help, but with little luck. I'm sorry, I don't know Harleys, so I don't know what model it was. You could probably get some feedback from him via email or the phone. It's Eagle Rider Rentals, the Las Vegas location. Hope this helps.
Terry