The keyway is gone, when I try to loosen the bolt, the engine turns. How do you remove the bolt in question when you do not have impact tools available?

Use a piston stop. In the absence of a professional stop, use a piece of nylon rope through the spark plug hole. Rotate engine to the point that piston is at bottom and on its way up, then fill cylinder with nylon rope about the diameter of a pencil or slightly smaller.

Hope this helps.
Regards, Don