Of the three Spinks. According to Bert Sugar, Louis management did not want to put him in there with light heavyweight Max Rossenbloom. Rosenbloom had an elusive slapping type of style, and was also durable. A tough guy to stop and sometimes out point. A pity he's not on film. Perhaps a wise move by Louis people as even if he won, he would not have looked good.
Its certainly possible with spinks. The wins over holmes proved to a degree he could mix with a solid heavy. Obviously holmes had seen better days and probably took spinks lighty in the first fight but he did pull it off twice. I hesitate to pick any one against Joe Louis but upset s do happen. Foster would be ko d as would dmq but spinks if he catches Joe on the right nite, well he would certainly give him a puzzle to work out imo