OK then.... never mind
The problem with the code V6X is it means different things to different models and years. I didn't realize you had a GC.
Grand Coupes had an option for a bodyside tape stripe treatment that you could get with the M31 belt moldings. Basicly, a thin double pinstripe like line that went down the length of the car near the top of the fenders.
Billboards couldn't be ordered with M31 in any event so you didn't have Billboards.