This just might be the Rarest Opel item.
consist of sparkplug wrench, sparkplug brush and point gapper, 4mm thru 19mm open end wrenches, combination philips/regular screwdriver, channel wrench, and lug wrench
No markings were visible. The leather was in good shape, still very pliable. The leather belt that rolls it all up looked very used. Some one posted that they had a toolkit for the GT but it had a zipper. I don't know if it would have been listed as an accessory. (???)