I would imagine they might expect that GT500 to be on the lot for a bit...lol. Nice price tag on that one...Works on any in-stock vehicle, any brand. Most OEMs give their dealers "floor plan assistance." Used to partially offset the interest paid on inventory financing, A lot of dealers will pass some or all of this on. Watch your calendar, too. The last business day of the month or quarter are typically better for deals.
But you'll likely get a better deal on a 120-day EcoBoost Mustang than a 270-day GT500.