Is that a Mach water pump pulley? If it is a Mach pulley, it is thicker at the mounting base. Try using a stock pulley. The stock pulley is much thinner at the mounting base. You will gain some clearance.
Its not a March, but very similar. Yes you are correct, the mounting flange is much thicker than the stock pulleys. I believe this is close to 3/16-1/4" thick. I dont have any stock pulleys, that is why I went to this set up. I have thought about getting a set of stock pulleys.