Trying to separate torque from HP does not mean anything because HP is simply RPM x torque. The original post says 2550 RPM in both cases, so the torque must be the same is the props are identical.
One minor issue - although the torque curve must be a bit odd for the two engines to give the same power at 2550rpm, an 180hp engine would be expected to develop more torque at lower rpm than the 160hp engine and will accelerate the propellor to 2550rpm faster, so I guessthe 180hp engine will be developing 'full' thrust for longer than the 160hp engine.