If I understand your system correctly;
You pull 3-350 phase conductors and a 350 grounded conductor in each conduit(based on a wye xfr., the grounded conductor (neutral) is derived from the xo post on the xfr).
From your first means of disconnect, you would bond the grounded conductor (neutral) to the enclosure. You then need to install a grounding electrode and grounding electrode conductor. The GEC that runs to the grounding electrode needs to be sized at 3/0.
However, that does not mean the ground rod. The ground rod only needs a 6ga. conductor. The other grounding electrode needs the 3/0 run to it. The other electrode would be the water pipe within 5 feet of the entrance of the building or the structural steel. Much confusion is due to many of us thinking of the ground rod as THE grounding electrode.
Hope this helps!
[This message has been edited by WebSparky (edited 03-28-2003).]