I have never seen a dyno sheet, but I would say about 400 ft lbs or more from 2000 to 3500 rpm would be a safe bet. Using HP/ Torque formula calculates 348 torque assuming the 265 hp and 4k rpm you posted. 440 rv engine would be similar. Both have anemic compression ratios and would greatly benefit from bumping them up. Do you need an engine?

Sounds like SP2P territory

3.71 Dana ? .... 70 ? I had two complete 3.73 Dana 70 axle assemblies up in northern Michigan... they are probably scrapped by now

What’s Your hoped- for MPG ?

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.

I have one 1972 413 short block, tough as nails !.....motor has low miles and #65 PSI oil press, windage tray, #452 head's , Lunati cam, edelbrock rpm intake , one of the best engine's i have had !

Ray, just my two cents, but if your oil pressure steadily climbs along with rpm there is little to no oil foaming to indicate a windage problem.

You can do a test by comparing oil pressure and rpm numbers running with a full pan v/s one quart low.

With the deep pans the RV engines have I doubt there would be much of a difference if any. No difference in numbers means likely no benefit from a windage tray.