Securing the PU while towing ..

[Gone-Camping]

You shouldn't have to buy both balls, the dealer should be able to tell you what that one has, about all he has to do is go out and read it, generally it's imprinted right on the coupler someplace.

 
Oddly enough both my father and myself had this same unit you're buying, his was a 1965 (same as yours) and had 1 7/8 hitchball, while the one I had (1978) had a 2" hitchball... go figure!