Unfortunately, but in my opinion, bite the bullet and buy a genuine Nissan head gasket. For the head, up your side of the world, I don't know anyone. However there is a guy in Alberton who sorted out my 4.2 diesel head for me, and all is well on my motor. The company is called Engine Rebuild Center ( 011 907 9476 ) Speak to Willem ( owner ) and tell him Cedric referred you, and he will look after you.
You can take him the head with everything in and he will do a pressure test to see if the head does in fact have a crack. He also won't bullshhhhhh you.
Something to be aware of, but I am not sure if the same applies to a 3.0 motor, but on the 4.2 motor it is SUPER important that the sleeves are either PERFECTLY flush or protrude the height of the block by a fraction of a mm. If not the head gasket rings don't seal properly and with the huge compression of a diesel motor you will get blowby, which could be what is happening with your motor.
Have a read through this...... Its a bit long but this specific post by Frans ( Touir de Frans ) mentions the protrusion. This man knows his stuff with diesels and specifically the Patrol diesels !!!viewtopic.php?f=44&t=1266&hilit=iron+maiden+died&start=40#p11358