Paul, it's difficult to explain without seeing the two in person..Yes the differences are so miniscule it probably doesnt matter.
The Saleen skirts, in the rear just under the scoop, extend upward more so then the Stalker skirts.. ( the Saleen sort of curve around the bottom edge of the scoop, rather then extend striaght across the bottom edge)
That and the Saleen skirts are more flush looking and straight.. Where as the Stalker skirts have sort of a lip or concave to them..
Basically both the same damn thing, with very minor differences.