I will make a wild guess that the original cardboard headliners were made in a press which pre-formed all of the proper and complicated curves in them.
I say this with a modicum of confidence, as I cannot imagine an assembly line worker fighting with a flat piece of cardboard like we are forced to do.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission