Hi all, In 99% of all 68's I have worked on (a lot!) and most 67's have the center bar butchered from the factory. Some were done with care but most were hacked up. In my experience, all 67 and 68's with A/C or Convenience were cut out. Some original cars with completely original interiors without A/C or Convenience had also been cut out. It is a factory thing and maybe some workers just cut the center bar on all cars in their shift. No rhyme or reason. They were Mustang's after all!
As for the dash sheet metal, 67 and 68 are not interchangeable. As someone above mentioned, the ashtray area is very different as well as the area around the steering column for larger collapsible column brackets. There are other small changes made to 68 as well. Such as mounting clip areas etc. Hope this helps. Paul