So here's the 4 mile object. Progress to date:
1. Figured out how to quickly generate a 4 mile object in L3DT Pro, decimate the polys down to an acceptable count, then export as OBJ, and import it into AC3D, with perimeter vertices at the correct 660 foot spacing. That took me 2-3 hours.
2. Once in AC3D, in order for both sides of the object to be uniform, figured out how to cut it in half and copy/rotate, so both sides are balanced.
3. Snapped all of the perimeter verts to grid.
4. Snapped all of the centerline verts to each other.
5. Found out there were some gaps at that interface, because I didn't plan step 1 too well. So I made some drape meshes (in yellow below) to hide the holes.
6. Started building the hierarchy. This is tedious, but once you're in a groove it goes quick.
If all goes well with the hierarchy, I'll post again with another step.