I have that model of enlarger but with the simple bulb-and-condenser head. For various reasons my lens board is a bit too long front to back such that pushing the lens to the back will not move the lens board enough to clear the front flange. (The one to the top in your pic.) If you loosen the two little phillips head screws in the front (top) that flange will dip down a bit, perhaps enough to let the edge of the lens board clear. If you take them out completely the flange bar will fall off and the board too. So be careful and mind where those screws fall, but doing this will not break anything in a normal 23CII; I've done it several times myself.