Using a quality ring compressor will make your life a lot easier when installing pistons. If you scribed numbers on each of the rods (one through eight), drop them into the correct cylinder bore. Once the piston is in position (the valve reliefs should be toward the lifter valley), gently tap it into the hole with a clean rubber mallet until all three rings are completely inside the cylinder bore. Never use a steel hammer. If anything more than light taps are necessary, check to make sure a ring hasn't popped out between the ring compressor and the deck of the block.