I have to restamp data plates for aircraft parts after they have been modified or upgraded. Folks that did free hand stamping back in the day had to know the positioning of there stamps VERY well. If they did it a lot then they got good at it. I use masking tape as the bottom line since not all surfaces are flat. I mark where the centers of each number need to be, based on the width of the characters, directly on the tape. I have center marks on each of my stamps. You can get a feel for when the character just touches the tape when positioning. After I have them aligned I giver er a good pop with the hammer. If a person has more time, they can get more elaborate about their layout but I've found that I get better results if I don't over think about what I'm doing and just concentrate on keeping things aligned in all three axes.
Reproduction stamps are getting more expensive. A person has to take good care of them. They are easy to damage even if well heat treated.