At SEMA, Gear Vendors introduced a bolt-in overdrive system for the FMX transmission, as used in '69-'70 Mustangs with 351W and 351C engines. The 0.71 overdrive setup includes all electronic components. Expect a typical mileage improvement of around 25 percent. You can also split gears, effectively turning the FMX three-speed automatic into a six-speed. The system uses a factory trans mount, and no mods to the tunnel or crossmember are needed. Gear Vendors Overdrive, www.gearvendors.com.