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If I had the desire to go thru it again, I might try a Cummins ISB 6BT swap but that thing weighs half a ton and is HUGE. It could be made to fit but the back 3 cylinders would be next to the drivers knees. and you'd be forced to run a cowl induction hood or no hood at minimum. But the torque and power of that thing propels 8000 pound pickups into the low 10s, imagine the speeds in something half as light and the fuel economy would be huge, driven conservatively of course.