I read on one thread that the AD trucks weren't perfectly uniform and that many of the body pieces were still handmade. The writer cautioned that replacement parts should therefore be thought of as an approximate fit only and we should anticipate having to work to get things to fit. I wish I could remember the thread I read it in - I think it was about patch panels for the cab.
Given that, I would imagine that the headliners are the same, but the trucks vary from (ideal) spec. It would be more difficult to manufacture products today that weren't uniform because the dies and set ups would have to change every time, adding cost to the manufacturing process.
That's my male answer syndrome take for the day (see Click and Clack for fuller discussion of male answer syndrome).
