I still think the wildest line I've seen was in the Ford Wixom plant. The same line built Town Cars (rwd frame), Continentals (fwd unibody), and then added the Lincoln LS (rwd unibody). They were all mixed coming down the line.
Nowadays, all the cars have common reference points and it's not so much of an issue, but that's just come about in the last decade+. They had to, to allow for more plant flexibility for volume slowdowns, popular models, etc.