No key operations are possible but it requires a tapered shaft and a tapered hub and both need to be lapped together. You have neither so if you want it to run you will need a key to fit the shafts slot and the rotors slot and they should be fairly tight in the slot. The rotor requires a wood ruff key on all my engines it looks like a half moon. If this picture is of your engine it looks to be wallowed out there is a good possibility your engine is done for with the way the key way looks there is ways of fixing it but you talk like you do not have the abilities to do the repairs that will need to be done. I suggest you get someone else to do the required repairs and or purchase a new engine. the one you have will be a tough one for you to fix.
You will need to machine a new key slot you will at the least need a dremel with a metal cutting disc and more likely need to split the case to get enough room to get the tool on the shaft to cut the slot. I dought if you want to tackle that. you might be able to use the damaged key way and hand make a special key to fit snugly on the shaft and the rotor both will take some work and you will not be able to buy the item off the shelf. So its your choice to do what ever you want to it. I will still offer my help but I can't promise I'll be able to make it work.
Take a picture of the rotor and its keyway if you can I'd like to see if its ate up like the shaft.
My thinking is that sudden stops, like letting the clutch out to kill the engine is what does things like this to an engine. If it was my engine I would try the JB weld and drive with extra care. If that did not work my next step would be to make a custom key that would take care of the extra wide key way. after that I would weld 4 tiny welds with a mig welder to hold it in place and leave the nut off if needed. A weld at 12 o'clock,then 6,3 and 9 o'clock. Yes there is the possibility of screwing up the seal but one weld at a time may be OK. From looking at his pics, I don't think things are as bad as he makes out but it's hard to tell.