Those were built in 1978, and they came from the factory with Birch veneer, in the "C" style cabinet (meaning they don't have the extra riser and plate between the top horn section and the bass section), and they had no finish on them. So whoever bought these, probably put the stain on that's on them now.
None of this is meant as a slam on your speakers, just passing on information that might help you understand the marketability of your speakers. These were close to the bottom of the line for Khorn cabinets and finish. People bought Khorns this way to save money, but still get the great sound of a Khorn. But the intitial savings do follow through to the resale later on.
Cleaned up speakers and good pictures will go a long way to getting the best price for them.
Have you tested them and know that all the drivers work? That is helpful information to a prospective buyer.
Good luck with your sale.
Greg