I had put a drive by wire engine into a GM before (6.0 liter gen III into a '69 Camaro) and imagine a Mopar would be similar. Assuming you are talking about an engine that is already drive by wire being retrofitted into your E body. You'll need the throttle pedal along with all wiring and computers that go with the engine. Just a matter of mounting the pedal to the firewall then.

If you are talking about retrofitting drive by wire to an early engine, I personally would not bother...