Create your file as TIFF or JPG with 300 dpi in the profile Adobe RGB 1998. Please include a B&W layer in the final file. You can leave this as it is or reduce it to the background layer. Alternatively, you can also create the TIFF file in the Gray Gamma 2.2 profile.

Tip: Proceed as suggested above if you are not sure whether the scan is really only B&W. Many times, the scans of B&W films are delivered as B&W in the format RGB, but they still contain some smallest colour information (scanner lamp). These are then visible in the print as color fringes.