I don't see why it would leak without reinforcing ribs. It is held down with 4 screws, that should be better than two nuts. I am guessing the two holes were drilled in the top because the wrong rocker arm studs were used.

Jerry, are you saying even with the 4 screws, the two nuts will warp the cover and cause it to leak? Maybe I will go with a normal 216 cover instead.