He'd beat Duran handidly. He'd have a close fight against Hagler he likely doesn't do enough in and loses a close decision. Probably the same against Leonard. Against Hearns he'd either lose a competitive decision or stop Hearns late.
Leonard is of course stylistically wrong for him, but SRL was neither in his prime or at his best weight at 160, so the question is if he toughs it out or if Toney takes over. Similar question regarding Hearns really - he could well get caught like Nunn. Vs Hagler... who knows, but fantastic match-ups all three. But Toney is just too much for 160 lbs Duran. Not only bigger, but also faster than Duran at that age.
Destroys Duran and definitely has a big chance of turning fight with Hearns into the Nunn fight. I’m not really buying that Leonard outclasses him because he wasn’t that good at 160. I’d make Leonard a slight favorite. Beats the crap out of Duran. Probably loses to Hagler. Of course, he’d underperform or be out of shape somewhere along the way.
Toney only became a complete fighter at 168. At 160: Toney wins a competitive decision against Duran. Toney loses a very close decision against Hagler. Toney-Hearns and Toney- Leonard are pretty much 50-50 fights.
At 160: vs 1983 Hagler - competitive early, Hagler takes over. Wide decision for Hagler - workrate, southpaw jab, stamina vs the Duran that fought Hagler - this is close, Duran boxes smart, but I'll say Toney decision. vs the Hearns who fought Hagler - Hearns decision, but a stoppage by either is possible vs the Leonard who fought Hagler - Toney close decision. Leonard style all wrong for counterpunching Toney, but he pulls it out.
In 1989. For this matchup you need to take the best version at MW. That would be 6 year earlier, when he boxed Hagler. Also, I don't worship Duran, although I recognize him as one of the GOATs.
Beats Duran via Comfortable UD. Beats Hearns via Late Stoppage (behind on points). Loses to Leonard via SD. Loses to Hagler via Competitive UD or MD.