Import and export the mesh out of Blender without any options checked and it's essential that you export his head out of Poser as a morph target with everything zeroed out.

Import Don's geometry file into Poser (everything unchecked) ... use the Grouping Tool & Spawn Prop to select only his head... and export his head as a morph target, uncheck everything else... you want to keep his head the way it is... unscaled, unchanged or anything except the morph throughout the whole process.