Help Understanding hitch ratings with a bumper and ball.

[dropanddrag71]

Heres what i am wanting to do.. I want to rent a u haul car trailer to tow my classic car from one location to another. The truck i have is a 70 3/4 ton, all stock, all HD springs. I have what i think is a dealer installed bumper with access to install a ball to tow with. (pic below).
I called to reserve and there asking things like hitch ratings, whats the decal on the bumper say about hitch ratings???
I am under the impression that with a ball on the bumper these 3/4 tons can tow almost anything!!
I haven't bought the ball yet, but assume all i needed was a 2 incher.
Absolutely no decals or markings anywhere on the bumper. All i can be certain is that grade 8 bolts are used to install everything on the truck bumper and brackets.