At the end of the day the thing you want to avoid most is damaging the thread up inside the crank.
Get a suitable 3/8unf bolt, something longer with a bit of shank on it. Screw that up in the hole so it has plenty of threads up in the crank but a good bit of the bolt poking out through the blade boss.
Get a nut the same size hex as the head of the 3/8 bolt for the nose of the puller shaft to go in, a small bit of grease or oil, your going to trash the nut. Hang a spanner on the bolt in the crank. When setting up the puller slide the spanner over the bolthead so it holds the nut as well. Spanner will do two things, hold the nut central on the bolt head and will stop the point on the puller shaft walking around on the bolt head. When you are winding the puller the spanner will hit one of the arms and that will stop the bolt screwing into the crank as you wind.
Then i stick a tyre lever down through the arms of the puller onto the body of the mower and start winding. It will either move or it wont.
Probably best to cut it off and buy a new one. I have had no luck getting them off in one bit, if you use a 2 leg puller and bolt you end up bending the plate anyway, it cracks it at the boss making it unsafe. I think they are $25-30 new, best i can work out from the pic its just a standard masport one.
Use a small grinder and cut in toward the keyway. Use a new key. You might have to cut both sides. Sit the shaft/motor on an anvil and try splitting the grinder cut open with a cold chisel.
Take care that you do not bend the shaft.
Cheers, Bob.
