The crankcase bushings on those Thors were known to wear out real quick if the oil concentration in the fuel wasn’t heavy enough.
Good news is they are easy to replace, since they are just an insert held in between the two steel stampings. Bad news is you have to machine them and make sure the concentricity of the ID to the OD is bang on. Use SAE 660 bearing bronze if you do make new ones. Don’t try to get by with an Oilite bushing insert.
There was an aluminum plate in between the rope sheave and flywheel as I recall on my former Thor.
Shim stock on the flywheel taper isn’t usually a good sign. It indicates that the likelyhood is very high that a previous mechanic has overtightened the flywheel nut, causing the tapered section of the flywheel hub to open up as it got forced too far downward on the taper. If you take the shim stock out and put the flywheel back on the crank with the magneto plate installed, you will probably find that the flywheel sits down too low, and makes contact with the coil heels or some other part on the mag plate. If this is the case, you are correct that one sure fix is a replacement flywheel. But you can probably re-use the shim stock and get away with it.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...