I think it's difficult to say how shaky a particular engine is just based on the observation in a given model.

Last week I was comparing two brisons 3.2, one in an 16 lb. Extra and the other in a 20+ lb. P-51. The Brison mounted on the P-51 was SO smooth, compared to the Extra. To test further, we changed the propellers, and the result was the same. My hypothesis is the heavier the plane, more smother the engine seems.

Of course it could be just a difference in production runs.