Towing capacity is dependent on a couple of things.
1.) the hitch on the truck.
2.) tire size and gear ratio.
3.) what the OEM says is the GCWR. ( gross combined weight rating.) this is the total weight of the truck, trailer, and contents of both. This includes fuel and people .
The TH400 transmission is a tough SOB. It's the exact same tranny used since the mid '60's in GM trucks. (sans bell housing pattern for Jeeps).
This transmission was used in a number of vehicles, including class A motor homes. The biggest factor in automatic transmission Longevity is heat and break down of the fluid. A good cooler is a must.
Another important factor is trailer brakes. I my state any trailer over #3000 requires brakes on the trailer. Many states are the same or close to it. Missouri being one of the exceptions.
Sorry I don't know the spec's for a J10.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.