From your post in another thread, you have a single cab. That means it is the lightest Ranger body. So that helps a little with payload.
Downside, shorter wheelbase is a little less stable when pulling a trailer. If you don't go real fast, no big deal.
If you want to max out the trailer load, I would strongly encourage you to get a trailer with brakes. Especially if you don't have a lot of experience pulling trailers. Heavy load, and hit the brakes on a curve, and that is called a 'jack-knife' and a very bad thing. If the trailer is heavier than the truck, it will start push the truck around.
An Explorer 8.8 axle is a good thing, if it gives you the gears you want. Should have rear disk brakes, which helps a little. But it weighs more too (good for traction and braking, but cuts into your load capacity). If you do the Explorer rear axle, get the Explorer springs as well. Will increase the capacity of the truck bed a little, although will ride somewhat rougher. The Ranger springs won't tolerate being loaded to full capacity for very long.
I'd probably look for a trailer with brakes, put a receiver hitch on the truck, and put the lowest rear end gears you can find in the 7.5 axle to start with (probably 4.10s). Unless an Explorer axle is just cheaper than gears for a 7.5.
And did you find out what gears are in the 7.5 rear?