The '40 class' two stroke engines typically include the following displacements, and possibly others: .40 .42 .45 .46 .47 .49 .50 .51 .52
Often, but not always, engines in this class fit the same engine mount and are very similar in physical size and weight. The different displacements are accomplished by changing the bore size and stroke within the same basic case.

Automobile makers did the same thing. The 'small block' Chevrolet V8 engine was introduced in 1955 with 265 cubic inch displacement. In the mid 1970s the engine had 400 cubic inch displacement but was exactly the same size externally as the original 265. There were lots of internal differences but not much externally that the average person would notice.