Do not be fooled by Roy’s record post 2004. Nobody in history beats him at 168 in his prime. Bet your life savings on it.
The easy answer for me is Ezzard Charles. We know he'd make 168 some time after the war and man would he be hard to beat.
1) Same but different. Lloyd Marshall. Unpredictable, a hard puncher who used strange angles and moves to upset the rhythm of his opponent. At his very best he would be in a difficult and wonderful fight with Jones I think. 2) Unknown. Harry Greb. Enormous work rate, iron-chin and he's not too small - he fought two very very close fights with one Gene Tunney while weighing 166lbs. Unpredictable defensive genius. 3) Boxing genius. Ezzard Charles. In 1947, Charles weighed in at 169lbs if we can stretch a point. After 1944, he lost only to heavyweights, and he beat more than a few. He stopped Marshall in the 169lbs fight; in the six months either side of this he beat Archie Moore, Billy Smith and Jimmy Bivins. I think this fight could be surprisingly crap as they both break up one-another's styles, but Charles has a good chance. These would be the three I'd go for and if I had to pick one i'd probably go for Charles.
In terms of guys who actually fought in the super middleweight division, it's hard to think of anyone who could have beaten Jones. The two most accomplished fighters in that division's history in terms of achievement were Calzaghe and Ward. I think they both could have presented Jones with his toughest career fights, particularly Ward as his boxing fundamentals were so solid and he was strong enough to handle Jones well if he could get inside. But even then, I can't see Jones losing.
It would be a tall order. Roy was out of this world at `68. Ezzard Charles would be a good one to go with. Perhaps Jake LaMotta. He wouldn't have to struggle down to `60. The Bull would be able to pressure Roy every minute of every round and use those rough tactics that sometimes worked on Sugar Ray.
Billy Conn for the first Louis fight came in at 174 lbs . And it was rumored he was really 169 lbs. So if Ezzard Charles name can be argued then so could Billy Conn.
Moore maybe? Probably not experienced enough yet though. Jones was incredible at 168 and the division is very young, so there are not many around to pick really. IMO to beat Jones you need to a) put a lot of pressure on him, b) be incredible good at cutting of the ring, c) have decent power, very good accuracy and timing and d) it would help to fight "off-rythm". To be honest Calzaghe actually fits three of those 4 points but falls short on point c. But wth his very high workrate he might eek out a points win. Unlikely and probably unpopular but possible.
I think Calzaghe is well in with a shout. I think Jones could well annihilate him, knocking him out, but I'd definitely give Calzaghe a shout.