M120 is quite a different beast in some ways to the meteor. Looks are different, mags are on the other end of the engine. Different pistons, and castings look different. Cam followers, pedastals are the same. I think the firing order is different, but not too sure. Oh and fuel injection, different magnetos and starter motor.
Recon it could be classed as the evolution of the Meteor, a bit like an Astra. Whether a 90's one or one from now it's called an Astra, but very different.