1. they are not all 32cc engines. their were a few sizes between the mm25,30,35,100,110,120,130,and the mm140. anywhere from 28cc up to 36cc.
2. the older cranks have a larger keyway for the flywheel. you can't use a newer flywheel on an older mini. can't remember the year they changed that. you can however change out the older flywheel onto a newer saw and have slightly adjustable ignition.
3. some of the older mini macs had a smaller pto side of the crank and took a screw on style clutch instead of the slip on and nut.
4. the muffler isn't a direct swap between the square style and the oval stack type between all saws. some will interchange but it's on some and not others.
you get to see all the differences working in a mcculloch dealership for 5 years