There's only a rubber sealing ring and the corrosion between the
aluminum parts which makes heavier to remove the distributor.
If the distributor body is stuck, losen the locknut on the end plate,
and pull up as far as possible. Apply WD-40 (or similar) to the stem
of the distributor body (where it meets the engine block rear cover),
and let it soak for a while.
Then try to rotate the distributor body clock / anticlockwise, in order
to free it up. When the distributor body (eventually) moves, you will
able pull it out from the engine.