The Saleen "Sleeper" GT was an official offering. I have the dealer order guide. The "Sleeper" was announced for both the Mustang and F150. Both were supercharged. These vehicles have a unique Saleen Monroney label and owners manual/warranty booklet.
These were offered on units in the Saleen pool. So, for Mustangs... cloth charcoal interior, IUP package, Shaker 500, wing delete, base painted 17" wheels, 3.55:1 gears. Unless a dealer would send their own chassis with different content.
Without pulling the guide out, some of their options were... painted GT deck wing, S/C dash pod, and the styling bar (convertible).