Rodinal,

The aluminum lens board does indeed fit over the lens. The little thumb screw at the top of it engages the notch at the thin end of the mirror and allows you to project your negatives across some distance to a wall mounted easel for mural printing. Be sure to reverse the negative in the carrier. Your should be able to get further details and even a print out of the directions on line, possibly through classic-enlargers.com/omega_enlargers.htm.Click image for larger version. 

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