I would look at the drivers door sticker, find the AXLE code, then look here:
Ford 7.5 & 8.8 Inch Axle Tag & Door Codes
You want a 3.73 or 4.10 axle for towing, especially with 31" tires
3.55 and lower are for MPG at highway speeds, which was common on 2WD 4cylinder vehicles, point of 4 cyl engine is better MPG.
This would be bad for towing.
Larger tires and axle ratios, assuming stock 2WD Ranger came with 14" wheels so 26" tire diameter:
3.73 axle with 31" tires turns into a 3.13 axle
3.55 axle with 31" tires turns into a 2.98 axle
So not sure the weight on the back end would be a problem, usually tongue weight is under 200lbs