I never heard anything about teaching Indians to knapp (that has the sound of an urban legend - like they couldn't learn unless it was real simple), but the apparatus you describe can be found in volume three of The Traditional Bowyer's Bible, pages 319-323. It's under the sub heading, starting on page 314, of "Forget Tradition, I Just Want To Make An Arrowhead". The description in the text is for flake over grind preforms. I haven't tried it myself but, starting with square edged plate glass, it looks like it would be more difficult than traditional techniques.