Hi Brian,
Try using the transfer vertices function in polygon or edit polgon menu to transfer the blendshapes (one at a time) onto your original head. what this should do is rectify the translation problem you mentioned in your post by bringing each blendshape back to the origin (ie. your base head's origin).
Do one at a time and simply export each shape out as a obj file and then undo to bring back your base head shape and repeat for all other blendshapes.
I havn't tried this but in theory it should work fine.
re Jim
Mayan elder......only in years.....