Well, a more usual PS grayscale export is gray gamma 2.2. However, you can't export from Lightroom as anything else but RGB, even if you are working in B/W. I have moaned about this for ages, but no-one at Adobe seems to like me (other than Eric, who is a good guy
). So I have to make a trip to PS to convert the image to grayscale and re-save my TIFFs.
John