Buddy could be a problem with his long left hook and good power,he outpoints the other two,though, if he gets mean he might stop Primo. Tunney remarked you couldn't miss Carnera with a right hand,and Tunney had a fast accurate one, that is probably underestimated for power.
Gene never tackled anyone of this size. He would probably handle himself well enough over ten rounds against Simon and Carnera. I would bet on Baer to turn the trick at 12 or longer. Tunney's abilities at heavyweight are the stuff of myth mostly.