For the sides, measure the radiator's depth. Add 1 inch and cut two pieces of MDF to this width and the same height as the front cover. For the top, cut a piece of MDF ½ inch wider than the sides and 1 inch longer than the width of the front.
On both side pieces and the front piece, mark for the screen openings: Draw lines 3 inches from the top and sides, 4 ½ inches from the bottom. Bore two ½-inch holes inside of opposite corners of the cut lines. Use these holes to start cutting out the screen openings with a jigsaw.