Importing big dae-files to opensim

Hi folks,
I have a big blender build - as dae-file 7.26 MIB - which I cannot upload as an entity. In similar cases I always proceeded as follows:

  1. I create an extra cube above the build in blender
  2. I export parts of the build, always using the extra cube
  3. on importing the files, I set the cube as root prim
  4. inworld I match the cubes by copy/paste the x, y and z axes
    This always worked great.
    But with my last build it just won’t work.
    Everything looks perfect in blender - but inworld the pieces just won’t fit.
    I am by now a little exasperated and would appreciate any suggestion and/or help!

I am running Blender 2.79 on Windows 10

Thanks, Tosha