hi luke
there are quite a few threads on this topic somewhere ...
differences I know of.. there will be more, someone else can add them
early cylinder head/rocker cover has oil pressure feed to the rockers, rockers and cam follower bearings are different. different carb and intake tract mounting to the head. older heads have bigger valves
counterbalancer shaft gears have different cuts
clutch is different
e start gears are different
crank is different
piston is different
Ignition and cover are different
clutch cover is different but can be made to fit .. newer one just has more mounting bolts
oil pressure relief spring rate and location are different, wire gauze oil strainer is different.
which parts do you need ? maybe it is an easier question for people to answer more specifically.