I am also trying to add dimensions to an isometric view of a simple cube. I have allow_3d_dimensions applied. I can pick edges and drop dimentions as usual, but they are not right. When you try to drop the dimention, you can select vertical, horizontal, parrallel for example. But if you select vertical, it gives you the vertical dimention of the isometric line. One edge of the cube is 200mm long, I just want to drop a 3d dimension which shows 200mm. The only one I can drop are stupid irrelevant dimensions.