I went both routes, the first time, I took a small DC motor connected to part of my speedo cable (the donor cable had broken due to being too close to the headers) and let it run for about 3 days. I then decided that the 85mph speedo just didn't look right, got a 140 and played with the pin and gears, took a little time, but not nearly 3 days (I recommend this option)!!
Gratz
Gratz