Not very. He'd win 2 or 2 1/2 minutes of each round with that superior conditioning. All he has to do is deal with an occasional flurry by Toney when he bothers to exert himself. And Toney is no massive heavyweight hitter and will have a tough time backing up Norton. Going to take a lot of effort and some quick feet to do that for each round.
Norton has his way with Toney. Toney would have never even considered fighting at Heavyweight in that era.
