Remove the rocker shaft if you haven't already, squirt about 1/2 cup of
motor oil into one of the cylinders, replace the spark plug and use a
socket and short breaker bar on the pulley nut to gently rotate the
piston up and push the head off.  Once it breaks loose you should be
able to rock it off.

Messy, but works.  This is a standard technique for removing MGB heads
which can rust to their studs.  You may have severely rusted studs too.
if so, replace them (a machine shop will need to do this) before
rebuilding the engine.

Stuart

'84 Westy and lots of MGBs