This from Sheldon Brown might be useful, especially the bit about checking alignment.
You can use a long straught-edge instead of string, obviously. It just needs to be able to contact the face of the dropouts, so you might need to make up a small spacer so it can do this while clearing the chainstay....
You can use a long straught-edge instead of string, obviously. It just needs to be able to contact the face of the dropouts, so you might need to make up a small spacer so it can do this while clearing the chainstay....