I'm moving this to the Windsor Power Forum. You'll get more responses there, and it's where this thread should've been started in the first place (not a flame, just fact).
Ford Racing has a nifty little chart to see which speedo gear you'll need, which of course is dependent on the final drive ratio. Installation is easy as removing the drive gear clamp down bolt & bracket, removing the cable, sensor, and gear (all comes out together) from the transmission, pop the clip off the end of the speedo gear, and slide the old one off the cable. Quoting Chilton's and Haynes, "installation is reverse of removal."
BTW, and out of curiosity, why are you asking about an '03 Mach if you have an '89 LX? Do you have a wrecked '03 Mach sitting around or something?
