on a 2t victa I generally feed a meter or so of fairly thick cotton rope into the cylinder and lock the engine, and hang on a breaker bar, sometimes they are just too rusty, and have to be cut.
If you have a (good) rattle gun its quite easy.
I havent had a 4 stroke give me major grief yet, a foot on the blade disc, and smack the L bar with a rubber mallet a good few times usually cracks them. (lets face it if a 4 stroke has been neglected to the point of the blade bolt being stuck in there solid, the engine itself is likely to be bad anyway.) a rattle gun is my recent weapon of choice for the main center bolt anyway, I have one on hand and they are just easier.
