Thanks Ian, that's comforting to know. I will have it skimmed - good idea.
These tools usually work by pivoting on a bell-housing stud and the tooth on the tool drops into the teeth on the flywheel.
I prefer not to use wood anymore. Last time, when trying to remove the crankshaft pulley nut before I hired the electric impact wrench, the wood block split and I had to fish bits out of the crankcase.