Second any problem with bridging the rear channels to drive the sub?
Thanks and any other advice is greatly appreciated.
Background: I'm installing a new system in a 70 mustang, obligatory picture

Speaker placement is limited to front kicks and a single center speaker. In the front kicks are PG TI 5 Elites (250w, 4ohm) and in the center is an Infinity Kappa 682.9 (100w, 4ohm). The rear channels are bridged to a Infinity 10" Sub (400w, 4 ohm). More details below.
