So I had a go with the new Blender 2.8 beta.
I was surprised to see its glTF 2.0 import/export capability, but it actually works:
1. Exported from 2018 Layout to .fbx (FBX201600) -> Import into Blender 2.8 -> Export from Blender to .glb (binary)
. - single frame export only (see bottom lhand in Blender export for option)
. - my glTF viewer (custom) seemed to display a not-so-cool darkening of textures
2. Exported from 2018 Modeler to .obj -> Import into Blender 2.8 -> Export from Blender to .glb (binary)
. - single frame export only (see bottom lhand in Blender export for option)
. - my glTF viewer (custom) showed a good end result
This is a much more straightforward way to get things done ...