Gen 3s are REALLY tempting but there's nobody home at low RPM. You've got to spin them to get torque and that's not where the Imperial lives. I needed to stick with the bigger engines.
BS.
My '17 Challenger has a bone stock 5.7, and it's done at 5500 RPM. I shift it at 5k at the track (6-speed, 3.92's) and it goes 14.0 at 103 on Tiger Paws, walking it out of the hole. The car weighs 4275 with me in it.
I get it, your Imperial is heavier. Hang a Procharger (or a turbo for that matter) off the side of a stock 5.7 and with a good overdrive trans of some sort, you will meet your goal.