If the tag is missing Isky used to make a small round calculator out of cardboard that had two wheels, one on each side. You could set your RPM and speed with the height of your tires and it would tell you what your gear ratio was. In fact it would tell you everything about your engine and gears. I have a couple that I have use for years and they are as accurate as any computer made today. I don't know if they still even make them, but I called several years ago and they sent me 3 new ones as I had just about worn my original one out and it was hard to read the numbers on it as some of them are quite small. It was easier than the turning the wheel one turn and counting the driveline revolutions, though I did that several times also. Any of the above methods works but for the driveline method to be accurate you need to know the range of gears that came in that years rear end. If the tag is still there that is the best.
Ron
