is it on the motor or off? if its off, put it in the oven when the wifes not looking and bring it up to around 300. aluminums expansion rate is 2 or 3 times that of steel and it should release some of the bite and let the plugs come out easyer. If that doesnt work, take it to a machine shop. We remove them every day at my shop, some will screw out, some you gotta drill out.Some will break loose at first and then start to get tight again after about a half a turn. If that happens, then the threads are going to come out with the plug.