I want to upgrade my oilpump with a tadpole relief valve. I know different stories about mounting them. One says, just place it and no worries. The other says you have to grind the tadpole in the filterhouse (likewise when fitting new valves in a cilinderhead) or the oil will drain back in to the drainpan.
Never heard of one. Though I assume the logic is the same as fitting a ball bearing instead of the standard shuttle valve.
If you are going to lap, then you will need to remove the head, strip it and flush repeatedly afterwards before refitting. You will have to prime the oil system as per normal.