Old CWO

Depending on the tire size, gearing of 3.73 or 4.10 can both be perfectly acceptable as your posted chart indicates. Assuming a tire size of 215/85R16, the 4.11 would run just about 200 RPM higher at 70 MPH than the 3.73 (2285 vs 2078). Given the application, I would personally default to the lower gear set all else being equal.

Ford 300/4.9L L6 is an interesting suggestion. They are well known for their longevity and make very respectable torque, enhanced greatly with some decent compression and a larger carb. Unlike the Jeep L6 engines, Ford's big six has the intake/exhaust on the passenger side same as the Dodge flat six. They also use the Ford Windsor bellhousing pattern so oodles of transmission options. Ford used them in trucks and vans from the mid-60s through the 90s so still easy to find. It is however, a long engine. I think it's something like 30" long. If the length will work, a good 300 with an AOD trans and deepish rear gears would make a dandy DD with real decent fuel economy potential. Pretty sure if I had a vintage F1 or F100 that's what I would be looking at for drivetrain.

In the context of refitting with a non-native engine, going from the short to long flathead Mopar 6 is relatively easy. In this case, that's a significant increase in displacement without dramatic alterations to the car.

She's a beaut! I really like that color combo

That was a really elegant solution for upgrading the front brakes. Bravo. Out of curiosity, what size are those rotors?

This might be a good time to think about converting to axles that use more common bolt pattern, tire and rim sizes as well as brake parts that are still in production. It wouldn't surprise me at all to find a dually GM 14 bolt or Dana axle with similar dimensions to your original rear under a much newer chassis. I'm thinking delivery van, mini motorhome, cab & chassis, stuff like that. The front will probably be a little more challenging but not unachievable.

There is a youtuber guy that runs straight Pine sol in his ultrasonic. The parts that come out of it look like they were hot tanked.

Sweet truck. Maybe give it the linseed oil treatment while it's waiting it's turn for attention.

One of the coolest looking and capable 4x4 trucks ever sold in the U.S. market. I wish I had the bankroll to buy and DD a stone stock long bed '79 Toyota 4x4. What an awesome little truck; it probably helped cement Toyota's reputation for American consumers.

Manual – Quality Engineered Components

I have a 52 truck 4 speed sitting in the garage that measures 7 5/8 inches. I am under the impression the earlier trucks are the same, perhaps someone more knowledgeable than me can confirm. You may want to double check your info on the AX15, IIRC Jeep and Dakota AX15 are 7.8 input shaft length.

Once you get to this level of fab and modification, I really think you should strongly consider just going straight to a V8. Everything you have to mod for installing a non-native L6 is pretty much the same as a V8 swap. Given the ubiquity of V8 parts and upgrades, your total cost might even skew lower.

Not Jeep T5, Chevrolet. The S10 T5 is adaptable to the Mopar flathead trucks with a fairly simple kit. The T5 was in plenty of 4 cyl. and V6 4x4 S-trucks. You would use the Chevrolet transfer case married to the T5. There's some interchangeability on GM transfer cases of that era so you have options. The GM NP231C is very similar to the Jeep and NP231 and just as reliable, even taking some of the same beef-up parts. Yes, the S10 T5 is NWC but that isn't really a problem behind a flathead. The NWC is more maligned than it deserves - the root causes of most issues are incorrect fluid and lack of positive stops on the shifters. Both of those are easily corrected making the NWC T5 more than fine for less than V8 applications. Yeah the AX15 is a better transmission if you can figure out how to mate it up but the T5 is low hanging fruit if you're keeping the old engine. Either way, please keep the board updated if you proceed. It's a cool project

I have pondered a 4x4 conversion a bit myself and would like to see one done similar to what you are describing. The XJ D30 high pinion front axle with factory leaf springs seems like a sound approach, especially if you already have the Cherokee rear. YJ, TJ and ZJ front axles could also work but XJ is in my opinion the best of the bunch. You would want a 95+ high pinion axle for the larger u-joints and lack of center disconnect. Keeping the flatty for power is fantastic but I'm not aware of an easy way to run the AX15 Jeep trans behind it. With available adapters, I think it is feasible to bolt up a S10 T5 in 4x4 flavor with associated xfer case. I would probably favor the NP231C with aftermarket slip yoke eliminator. With 4X4 trucks, tire size drives almost everything so pick your last set first. Given the strength of the drivetrain proposed, 33s would be absolutely the maximum reasonable size. I like the idea of narrow steel wheels and LT215/85R16 in a very aggressive tread pattern for that old school skinny/tall look you would see on early 4x4 trucks.?

I have installed three-point retractable seat belt systems in vintage cars using a kit from this company: Seat Belts (julianos.com)