Yes, 3DSimEd can do the job. Import as object the gmt. With Ctrl key pressed, capture the entire geometry dragging the mouse with sx (first) button pressed Move the pointer on the geometry and press dx (third) mouse button -> objects menu -> reverse faces
Sorry for the late reply guys. @ 2Slow4u; thanks mate, that worked! I also had help, but had to try this myself too; learned something! Blender can do all 3DSMax does? Good to know. But the question what I don't get about blender........ehm, what DO I get I can do very little with it. Spend months just replacing a pylon. Its not my cup of tea. I think making a car, takes me years, hehe. Thanks guys.
Worth watching this short video to see what Blender is being used for these days: The Man In The High Castle