The blade boss is easy (at least in theory). Use a puller bearing on the temporarily loosly re-installed blade bolt to pull it off.
After it's off, DISCONNECT SPARK PLUG then have someone pull in the engine brake control and rotate the engine sing the start rope. If the crank rotates off-centre, the engine is scrap.
If you need a replacement engine, drop me a line at ;-
phil_saunders (a) bigfoot.com
Phil Saunders, April 2009