I think regardless of how old the cat is, how old the basenji is…. you ALWAYS have to keep an eye on the two. Make sure your cat has a safe place to run to in case your basenji pup doesn't understand that he is not to think of the cat as prey. Basenjis are hunters, and that is a natural instinct for them. We have a very tall (8 foot) cat tree that has various sitting levels that Kipawa cannot reach.
Also, your basenji might try digging in the cat litter box - many of them love to dig. So you might want to try to find a place your pup can't get to it, and hopefully your cat will accept the change in location. Or if your cat doesn't mind it, one of the covered litter boxes might be a suggestion.