Hello,
sorry at the moment i have no OFP running to look up the coordinates. But the east castle ruins are on the east side of the lake in the middle of Nagova.
That lake have a big bridge at its south. And an island in his middle. You start on this island. So the castle is south east of the starting point.
The west castle is in the desert in the west of Nagova. Near the occean. Can you find it ?
If not i will look up the coordinates.