Great site ya'll have here. I am always on the look out for a great place to learn.
We are working on a 61 unibody without the wraparound back window. We ordered a headliner and is dimensionally different from the original we took out. The supplier claims that we have an odd ball truck...that does not seem logical.
Hereís a link to the project if it helps
It is possbile that someone replaced the headliner with the wrong one to begin with. Hence your dilema concerning the headliners not matching. I did some searching and came up with 4 different part #'s for the liners. 2 specificly for non wrap around rear glass and 2 covering 61-64. So there is a chance of the wrong one being put in before you got ahold of it.
Well there is the custom approach using fiber board from homedepot as posted on another thread. May not be quick but you have the original one to go off of. If I am right the fiber board will in fact be thicker so it will last longer. Just a thought.