[Mr70]

I can not confirm what exactly yours came with Bill,but I have seen early Chevelle/Elcaminos come with OB stated in box 19,and their driveshaft had one stripe Orange,the other Black.BU was usually Blue.The 2 might mean two stripes,as some had one,others three.
I have various 1970 L-78 Elcaminos showing OR-BLK,built with M-21 transmissions & 3:55 posi from both Atlanta & Kansas Assembly plants.
Before 1970,these codes were vague and brief.BY would stand for Black & Yellow.
In 1970 and later,they started being more specific across the board with these codes,and used BLK for Black,BL Blue,BN for Brown,PK for Pink,OR for Orange,YE for Yellow & GR for Green.
Baltimore was odd,in that they used their own 2 letter unrelated system that I'm still trying to figure out..