Not sure how that works with companies like Saleen, Shelby, Roush, etc...
These days so much is done in the computers that they may already have enough specifications and CAD info to actually build pieces to cast off of and fit parts. Saleen may well be to the point of having parts ready to produce or already have items waiting to bolt on when the cars ship.
Saleen owner/followers interested in buying the 2015 may be able to get them in November if all goes as scheduled with Ford and they ship in October.