The standard package fitment is to locate the linkage above the right hand throttle body as this location is the most likely to give a clear throttle cable route. It is also easiest to adjust when above the throttle bodies.
Some may, generally for aesthetic reasons, prefer a linkage mounted below the throttle bodies so this is also available. However, be sure that the throttle cable route is possible as many engines will have interference issues with alternator / water pump belt drives when the underslung linkage is used. Optimum throttle cable routing makes a great improvement to pedal feel so do not compromise the throttle cable routing.
Twin cable linkage are available for race regulations that require them. These are only available for mounting above the throttle bodies. Unless you are required to use twin cables we advise against it.