And there be the problem. The ancient alien hypothesis does not stand up to close scrutiny.
It really doesn't. I've seen 'evidence' to back it up shot down time and time and time again on these boards over the years. With that in mind, I really don't think anybody is going to be able to present something that will convince you, Graham. Someone might try, but unfortunately, it won't take too long for whatever they come up with to be amiably demolished by members here.
What bothers me most, is that when this stuff is dissected, and shown for what it is, people still insist that it's kosher. Which is a bit like a Young Earth Creationist being presented with geological evidence of the age of our planet, but stubbornly sticking to James Ussher's chronology.