I’m pretty sure the MDF was 19mm which is pretty close to 3/4". I’ve resurfaced mine a few times though, using a wide flat bit to machine out the area covered by the cutter and a wood plane to remove the shoulder left around the edge where the cutter cannot reach.
I’m due to replace it all very soon because there"s only approx 1/8" left between the top of the centre rail and the top of the wasteboard - I’ve already marked the metal with a tool bit,although it did little more than remove the anodising.