So I presume the shear pin (key) was not inserted right or broke and this caused the crank to wear the main pulley or even wore the crankshaft end. Using JB Weld to fill in the worn area is not really a permanent fix in my opinion, but who knows! I am guessing the other part is wobbly because maybe you guys did not get it centered perfectly, but I would run the thing till it goes again and that could be a long time. It looked like this.........................
Another thing you could do is make a new keyway 180 degrees from the original with a dremel tool or die grinder and mount the gear 180 off, but that would require some precise measurements.
In the meantime, maybe locate a crankshaft, main and rod bearings,crank pulley, seals, gaskets, etc so you have the stuff you need on hand.