... who fought for a world title. (World ranked: Has appeared in The Ring's top-10, end-of-year ratings).
I think I understand what you’re asking for here, but to be clear: You mean the first boxer to fight for a world title who was the son of a ranked boxer (presumably not at the time, but was in Ring end-of-year top 10 during the father’s career, at some point earlier than the son challenged for a title, right? You don’t mean first son as in first-born son, correct?
I’ll go with Brian London, although it probably happened years earlier. His father, Jack London, was ranked and Brian challenged Floyd Patterson in 1959 (and later challenged Ali).
Can't be 100% sure, but I think you got it on the first try - at least I can't think of anyone before Brian London (though I would be happy to be proven wrong!).
