Since the Nemeth Code has no format for this, I agree with you that your best option is to reproduce what you see as a graphic. Yes, use a spurred line or other type of tactile line rather than braille dots for the box outlines. Use the same measurements and proportions you see in the print copy. The numbers are centered to their boxes in print, but you should check the new tactile graphics guidelines for location of these four numbers in braille. There is no need to put an general omission symbols in this drawing.
Thank you for posting your question.