Man, I once found a site that had a calculator for this. I'll try to find it again. And somewhere in my great archive is a Super Chevy that shows you how to do it and lists all of the available gears. But neither helps you now.
You need Tire OD, Gear ratio and how many teeth are on the speedo drive gear on the output shaft. Usually you can get by changing the driven gear (the one that comes out).
Man, the 92 still uses a cable? Damn old cars.
