the case on the left is for a NOI
the case on the right is for a eureka FLEX 'radial fin'
the motor mount bushing is the tell.
put the cases back together, and you will see they are not the same width; the flex cases are much narrower.
the crank is smaller as well as the output gear and i think maybe the clutch bell is different too. and maybe the clutch cover?
some people think there is a performance advantage to using the narrower and lighter output shaft gear.. I say leave the garelli's alone!!!!
good luck on your build ;)