If you are sure that all the bolts and nuts are removed from the head (some bikes have a small locating bolt at very front or back of head that attaches head to barrels, not sure about the 500).
Being me (part caveman) I'd use small wooden wedges spaced around under the head and tap them in sequence to raise the head right off but that's just me.
You don't say if the engine is still in the frame or what sort of damage you are trying to repair, could a piston crown that had disconnected from it's piston be locked onto the head or tied up with the valves, nasty thought I know but seen it on other bikes.