Though I never really gave much thought to it, whenever I've been relocating and rescaling .sur files with my utility (yeah, I know, shameless plug) I always take the numbers straight from MS3D and feed them to the utility. Now, for only scaling it should of course be the same, but for relocation it's another story entirely. Since the utility doesn't have anything to do with MS3D, I would venture a guess that the units are the same. However, if this doesn't seem to be the case, build yourself a cube, export it, and then check it's size with another program (HardCMP would be a good choice, since you can place hardpoints anywhere on the surface of the model very easily, thus allowing you to know the x, y, and z coordinates of the faces of the cube). Once you discover the size of the cube, just go back to Milkshape and rescale appropriately, then export again.