The AOD four-speed automatic is the best choice for about 95 percent of street-driven vintage Mustangs. Several companies offer new AODs, like the Lentech Street Cruiser unit shown here, which includes a 12-inch non-lockup torque converter. Other sources for quality AODs include Performance Automatic and B&M. Of course, you can also get an AOD from a Fox Mustang donor car, but it's more of a crap shoot with a used transmission of unknown condition. It may need rebuilding before it can be used.