There are definately two different 8k tachs as far as redline colors. I don't know if we can ever figure out the exact reasoning, I would be VERY surprised if it tied into BB/SB. I would say most likely it was two different vendors? Are the 5 digit vendor codes different on them? Aside from alot of 72s have 8k tachs with the resets through the plexiglass, I had a somewhat early 72 Rallye with resets throught he woodgrain, and date codes on everything showing it was original to the car.