Gear vendors o/d by itself won't get you there. Gear vendors and a high efficiency a/m torque converter would be very close with current gearing.

518 with lockup would be right on the nose as well, but you would have to rig some vacuum/ electric signal to turn off the lock up when pulling any kind of grade or lowing to protect the lock up converter clutch. An adapter for a 618 to mate behind the 413 would solve this problem as lots of diesel converters out there have triple discs. 518 non lockup with high efficiency converter would work and avoid the headaches.

If you consider changing the gearing, I would rather do a used factory set up rear than a gear swap. I hate listening to a whiny rear end on the highway. It is like the equivalent of listening to an ex girlfriend, or Doc, for hours on end.

The heads are an absolute at this point. Took a couple valves out of mine, and there is NO stem or seat wear at all. Clean enough I may not touch the seats other than lapping them unless I decide to do a 3 angle. Factory purpose built parts for the application that are damn near free are a no brainer.

I am going to do some tuning of the stock set up following Ray's lead on that. See what can be done with it, then swap my frankenstein 440/413 headed monstrosity in and do some direct comparison tests. I like tinkering and improving on what ma mopar did to test the limits.

Question for you Ray. Have you had any issues with ethanol gas- vapor lock, hard/no start when hot, etc when driving in hot weather? I am spit balling an idea of having dual gas tanks, the second to run ethanol free gas (90 octane here v/s 87 regular unleaded) to help with detonation if needed and to run the generator to prevent carb issues. Could also run it the last ten miles of any trip to keep that garbage from sitting in the carb bowls for any period of time.