Next phase: Attempting to use buildings on the game engine side which were created by blender-osm, and then exported from Blender into T3D.
Clearly the heights are going to require some code tweaking if this is how I end up doing it, and I need to get far enough into osm2city to figure out how to dial down or remove the peaked roofs. But the good news is on the horizontal plane, the sizes all lined up pretty much perfectly on the first try!
After all that works, then we get to deal with the textures.