Hi Bergy,
It is difficult to tell what has been swapped from just the pictures. The only other distinguishing feature I can see is a paddle kill switch on top of the head. Of course, you can also see that the spark plug doesn't come with a boot.
The hacked-up cowling indicates a need to free the governor linkage to stop it from binding.
That is some obvious tampering/modification. Perhaps the problem is a different type, bent or custom/homemade linkage?
It is rare for the bore to be in good nick after so many years, unless the engine has had regular oil changes and the air filter has been cleaned/replaced often. To refurbish an engine of that vintage, sooner or later you'll want to remove the cylinder head anyway, to check the condition of the bore, piston, rings and valves. Afterwards, you'll need to decarbonise everything before reassembly.
