The speedometer error is really frustrating. The worst part is that it was probably built this way on purpose. I recently changed my speedo so now I don't worry about it anymore. The gear drive converter would also alter the odometer and trip meters. Although my speedometer was 10% out, my odometer and tripmeter were dead on. If I'm not mistaken other poeple have found the same thing, so the drive converter doesn't really sound like a great solution to me. Altering the magnets is probably the way to go if you can manage it without doing any damage. For $300 you can get a dakota digital unit that has speedo, tach, trip and odometer, 0-60 and quarter mile times, and a buch of other features.
http://www.dakotadigital.com/Detail.cfm/-/Category=66/PartNumber=HLY-3016/product.htm
