I am part out a Honda GX620 engine that was a repower for a John Deere 318 lawn tractor.  It is up to you, and you alone, to determine if this part fits your engine.

Honda GX620 drive shaft coupler.  This is in excellent shape and worked perfectly as shown and from a Deere 318.  It mounts to the flywheel and connects to your Deere drive shaft.  It is 1/2" thick.  Thanks.