That looks to be a pretty big gap - Do you have the cork end gaskets in place? If so, take them out (I use black RTV silicone and never mess with the cork) and measure the gap. You can get thick gaskets +/- .125 (about 1/8") but that's the only real quick fix. If it's greater than .120" you may have to have the ends (aka "China Walls" ) milled down which means a tear down of what you have done and taking the block back to the machine shop.