I had some 747's, they were my first clipless pedals. EXCELLENT pedals, as you know. Unfortunately, they don't last forever, I retired mine several years ago, and in fact they were doing the same thing yours are doing (clicking, clacking, more play than should have been, etc.). Sometimes pairing new parts with old ones makes the wear more evident, as is the case with your new cleats and the old pedals. Maybe someone else has an idea on how to rebuild them, but my opinion is that it's time to shop for new pedals-