Working with grayscale images

I'm working on a book that will be published through Lulu which recommends that black and white photos be set for Grayscale and gamma correction 2.2 to 2.4. (If you are printing a color book that includes black & white images, the black & white images should have the color space set to grayscale.
The gamma of a grayscale image should be between 2.2 and 2.4.)

If I set the color space to grayscale and do a manual gamma correction of 2.2 through the  Image --> Adjustments --> Exposure, the photo lightens considerably. If, instead, I apply the color profile gray gamma 2.2, the photo darkens.

My experience in the past with including Black and White photos in a print publication has always been that they print darker than expected, so I have to go back and lighten them after looking at printed proofs. Lulu is the first publishing entitiy that has provided guidance for grayscale images. My question is, should I use the manual gamma setting for grayscale images or should I trust the profile to output well-rendered grayscale images?