Heres a 66 seat that was listed on ebay. Haven't seen one in this color yet. Maybe one of the 66 guys can lend more info on if its stock color or not. Has a build sheet still in the back. Not mine....but pricey
Link:
http://www.ebay.com/itm/271420479134...84.m1423.l2649
Also appears to be GMC sill plates...was there any difference in the GMC/Chevy deluxe seat color options?