I agree with Northern Thrux on the use of the Fumoto valve.
Here's a link to Pelican's correct cover for the later oil pumps.
Porsche Oil Sump Plate Kit With Drain Plug For Use With Turbo Or 993 Oil Pump
Ebay also has one that is simular to the factory cover but with a drain valve.
Porsche 911 930 74-83 Engine Oil Sump Plate With Drain Plug