Ford Mustang 41X
No one really knows how many Fox-body Mustangs with trim code 41X were made, which is a big part of its appeal. This 41X is possibly the rarest part of Fox-body Mustang history (via Motor Trend).
The 41X is the trim code for stripped base LX models with a 5.0 HO engine and manual gearbox. When the 5.0 HO became available, serious drag racers wanted lighter cars for drag strip duty. So they ordered their base models with top-of-the-line engines and no equipment. Cars delivered this way got the 41X trim code. They were extremely light and mainly used for racing.