Just returning here, thanks, will look and try. In the meanwhile, I'm learning about a less manual approach, will have many of these to process in building out the cave, using matchmove to "create and modify survey constraints". That functionality within matchmove allows me to establish a common scale and coordinate system between the meshes. I still have to locate the 3 common points of reference (many more if scaling across the mesh isn't consistent, which fortunately it appears to be) in the overlapping region of two meshes, but from there it's fewer clicks. Big thanks for great tips.