From someone who tows a lot with his 2.3L I'll chime in on this.
Is it technically illegal? well, technically, yes. You are over the max rating. HOWEVER, all models ran the same brakes (with the exception of 9" drums vs 10" drums), same frames, same suspension, same everything. Having extra brakes on the trailer will be a huge bonus as well. It may be slow, but it'll stop just as well as the more powerful trucks with higher weight ratings. Personally, disk brakes are a bit overrated. The drums stop you plenty, my rear axle chirps quite a bit now since I put the Explorer axle back there, nice to know the ABS still works.
A 4.10 rear axle will definitely help, and while not a huge difference gearing wise, you can easily factor in a L/S differential and the 10" brakes with the swap too. All 3 of which will provide a much better axle. You probably have a 7.5" currently as well, this should also upgrade you to the 8.8"
If you can deal with the way the truck looks, try small tires too. This will also help with starting out loads. Just make sure they've got the weight rating to handle the trailer and bed load, and try to get a set with some multi-ply or at least stiffer sidewalls to help control the trailer.
Even though the manual is the lesser rated transmission, it's universally considered to be far more reliable. And it's the same manual behind the 4.0L, which holds up just fine except for the most abusive of drivers. Most people don't know how to drive a clutch, and will easily burn one out trying to tow.
Dropping off (both pics before axle swap, with 3.73's)
~180 miles in the middle of the night. Just South of Flint Mi. to Big Rapids Mi. We also put the front clip back on, stacked my bed flat. Stacked a bunch of stuff in the J-10. AND had my friend in the passenger seat.