The Vanishing Headbox (regardless which version) is a great classic piece and given how much time has past since Val tipped it, I don't think you'll have any problems. However,[begin short lecture here] it does not matter if people know how it works so long as you are able to present it in a way that entertains them and can still mystify them.
Not to go into a long tale but years ago the L.A. Times did a feature story on Johnson Products... in the article was a color pix of the Cigarette Thru Quater gaf... one of my pet pieces! So, thanks to some quick thinking I still did my "signature" routine at the Castle, using that article as my close-up pad and asking folks "How in the heck could I have done all that using something that clunky? Don't you just love the way the media contorts facts?"
The moral of the story is DON'T SWEAT THE SMALL STUFF! If you like this or any effect, make it your own and in doing so, learn how to do it better than anyone else. Your audience will appreciate it and not think a thing about what they saw some jerk do on Tv (unless you're doing a show for a room full of jerks... that does happen... but it's rare.)
Best of luck!