if the previous monitor brackets are still there, cut a piece of 1/4" mdf to fit the area so you can use the tube mounting points to mount the board.
then just drill 4 holes for your VESA mount on your monitor and screw it to the board.
90% of the time the fit between the monitor and the glass is perfect, as often the monitors had about 1 1/2" of space between the mounting tabs on the frame and the front of the tube which is about perfect for an LCD.