I don't know your exact model, but most are precision machined fit, so may take a bit to remove due to rust etc. If you take the starter motor out you can get a brass drift in there to give it a whack, then a socket on the front crankshaft nut and rotate and whack again etc. This is of course after having removed the bolts!
Edit: And don't forget the usual safety precautions when rotating an engine so that it doesn't accidentally start, like ensuring fuel is cut, stop leaver pulled if it has one, IGN off, etc., etc..
If you don't have a brass drift, a bit of wood, prefer hardwood. YMMV.