Problems with UV Map

Hello all,

on the pic you can see two of the same meshes. I have tried to make a UV Map for both. But the uv Texture for the right one doesn’t fit. Both meshes have the same topologie. The right mesh is the box to make
the Normal Map. The left mesh is equal, but a little bit smaller. It should then be the lowpoy mesh for my project. How can I make shure that the UV Maps for both meshes fit?

So I might have a solution for my problem. First I have made a UV Layout from the mesh that I used to create the Normal Map. I exprted the UV Layout as a png File. The png File was used then as a template for my Lowpoly mesh. I think the result is not so bad. I unwrapped the Low Poly mesh and layed it over the template.
Especially the areas where the rivets are placed is pretty proper. I think I can optimize a little bit if I use some more seams.