Did you any remaining pieces of headliner?
Was there a cardboard headliner in the "cab"?
Most likely, "yes". Are the contours at the rear of the "cab" roof the same as in a regular cab (on the rear side and at the rear back)?
Was there a cardboard headliner in the rear? If yes, do you have the mounting cross-ribs/strips?
If any pieces of headliner are remaining, can you post photos? I do not see any in your Photobucket album.
Good luck - please keep us informed of your progress.