The 275s and a "plug-n-play(aka: VA Box) will probably be enough power to hurt your stock transmission... if it was me, I would choose one or the other til I modified the transmission.
The BD brake can be installed on just about anything, but be forewarned that Dodge does NOT recommend putting exhaust brakes on auto trannys... they made Cummins do a "buy-back" a year or so ago... paid back the cost to the consumer. With that said, many members are running an exhaust brake with an auto... I am sure some of them will chime in and answer that one better.