The article also suggests that 6 (yes, six) different engine options will be available for the S550:
EcoBoost 5.0 Coyote Engine for the GT500
N/A 5.0 Coyote Engine for the Boss 302 (and presumably the GT)
EcoBoost 3.5L V6
N/A 3.7L V6
EcoBoost 2.0L 4-cylinder
I'll believe it when I see it. The EcoBoost 3.5L and the N/A 5.0L occupy essentially the same position, as does the EcoBoost 2.0L and the NA 3.7L.