Caveat: This is something I read many years ago and I can not remember the source. I do think it is at least somewhat true.

When the 68 B bodys were designed the 2drs and 4drs were given mostly new (and lower) greenhouses but the wagons and convertibles continued to use the 66-67 greenhouses. This was done because the lower volume convertibles and wagons could not justify the tooling cost.

I have owned a 68 Coronet 500 convertible and 440 wagon for many years and have many times used pieces from 66-67 B's when parts off of 68-70 2drs/4drs would not work.

Carmak
Riverside, Iowa