There is a reason that most of the 2 stroke scooters today use a minarelli style engine.
Tomos had 1 common engine until the 90s.
Puch had 2.
Minarelli had at least 5 I have heard of and had there thumb in a bunch of other motors. They were constantly refining and remaking their engines. From a business standpoint it was folly to keep changing designs and not making all the parts compatible, but from an R&D stand point keeping the same basic design for 30 years is foolish.
Minarelli just happened to have the best design and experienced designers in the mid-late eighties when Yamaha wanted to break into the scooter business and didn't want to try and compete with their tired shaft drive set up that even in those days was slow.
Cool engine for sure. Did those make it to the states at all?