Sure, you can block off the outlets with no ill affects. As for how, the one on the intake can be plugged with a simple pipe-plug. If you look around, you can find one with an allen-head so it won't look like you accesorized your car from the plumbing department at Home Depot. The outlet on the water pump might be a little harder, since it's typically pressed in, but if it were me, I would remove it and find a brass freeze plug that's the same size. That way it'll match the ones you have in the block and heads and look like it belongs there.