I think I may have answered my question. The only other components in the stylus holder apart from cantilever, stylus and suspension is the compliance adjustment screw and the suspension filament.
Therefore the only difference I can see between the ML150 stylus and the ML180 stylus is the cantilever material (boron tube vs Beryllium) and size of microline stylus (0.08 vs 010).
Therefore the only difference I can see between the ML150 stylus and the ML180 stylus is the cantilever material (boron tube vs Beryllium) and size of microline stylus (0.08 vs 010).