there is another way.....
there is a unit that will adjust your speedo for you without changing anything. It is a simple hook up that you put into the speedo feed from under the dash. My son got it from someplace and with a hand held "GPS" you can get it down to the right speed. Best part is that you can move it to another car if you sell, or if you change gears again it can fix you right up again. It has a endless range of adjustment, as it did do a set of 4:30's gears for me...........Rich