Every hole needs a plug. I can't remember how many plugs there are, but it's at least 8. 3 on the back of the block, 3 on the front, one near the rear main bearing cap, one on the driverside rear of block where the deck surface is (the cylinder head has to be removed to install this one), and there might be one or above the oil filter mount on the outside of the block. These are thread in plugs.