Cylinder head unbolted but not free!

Assuming you're absolutely sure all of the fasteners have been removed I found a nylon drift and a focussed whack, sorry measured impact, with a hammer was a more effective way of moving it. A soft mallet is more difficult to target.

You could always try the old trick of removing the plug, set piston at about mid stoke, feed sting through the plug hole and when full, crank the engine. I have never tried this but something like it is on one of the heavy twins videos, I think.

If you are going to use the string method as Charles recommends, be sure that you start on the compression stroke such that the valves are closed.  You don't want the wad of string to bend a valve.

  Mike

I have loosened mine by running the motor with the bolts slack, but a 2x2 timber under the exhaust port and a good whack  is the usual method. 

Or, a bit of lateral thinking!  If the engine was running, replace the 5 head bolts, leaving them with a little slack, then start the engine.

If the motor is out of the frame and you intend to entirely strip it, take the head and barrel off as a unit.                               Lay the assembly on an old cushion or similar. Knock the head free using a piece of 2x2 timber through the bores. This has worked for me on a couple of occasions, but if your motor is staying in the frame you'll have to stay with those suggestions already offered.

Assuming that you have removed ALL of the fasteners etc, old age has probably caused the joint to glue itself together. Some all round gentle heat from a hot air gun or the better half's hair dryer around the joint might do it and shouldn't cause any damage or affect the castings. While its hot a few sharp smacks should be sufficient to break the "stuck-tion".  Once you get the joint broken you should be able to tap in some soft wedges, (plastic of aluminium) to part the faces without damaging them. This is a common problem on old face joints that haven't moved for decades and is best done with a copious amounts of patience.

.. Chris!

I had this problem with my model 7.  I couldn’t get the head off, but the barrels and head together came off the crankcase.  I put them on the barbeque on the other side from the burner, lid down and kept an eye on the temp.

Took them out, refitted to the crankcase and tapped gently under the exhaust ports and off came the head. 
Sausages didn’t taste so great.

Did it come off, John?

You have counted all ten, haven't you? Including the last one at bottom dead centre underneath the carburetor?