Still not seeing it, lol. I guess you mean it would be their 69, except that you need one to be the upside down version of the other...? I don't know. Someone should write a research paper on this. :D
Unless you're meaning it specifically has to be 2 digits, and therefore XIX doesn't qualify? If so that's fair (it was just the closest analogue I could think of. Maybe II would indeed be better).
I can't believe I have to explain this, but the key to 69 is that the two "people" are in opposite directions to reach other, not that the pair looks the same from either direction.