That info was wrong as the starting point. The factory stock unrestricted base engine in the 2015 GSX-R600 bike appears to be making 125 hp @ 13,500 rpm and 50 lbf-ft @ 11,500 rpm. This is the best official info anyway. It’s likely ball park correct because other 600cc four cylinder Japanese bikes made similar power numbers at the time.
In my opinion, a reasonable expectation as a starting point is to shift the same torque peak value down, by a hook or crook, from 11,500 rpm to 9,300 rpm and make 50*9300/5250 = 89 hp. @ 9,300 rpm.