Leitz flash sync, black scale flash sync numbers, chrome bumper added to shell, if the camera was WW2 the film speed dial is updated to newer B setting, often the vulcanite covering is changed to IIIF/M3 style vulcanite covering.
Have to look at each camera to figure out if it's a real factory conversion or not, many cameras were cut up or had mods added by photoshops in the late 1940's early 50's and this effects the value of the camera, factory modified cameras are much more valuable than third party modified/photoshop cameras.
Tom