Changing black color space when converting from greyscale to cmyk

In PhotoShop 6, how can I change the behavior of the conversion from greyscale to cmyk? I need for 100% black to remain as 100% black after the conversion, I wind up with 75C 68M 65Y 90K. Because of the gradations in the image that I am working on, I can't convert the image and remove the unwanted colors because the conversion changes the gradation values when it adds the other colors.
Thanks for your help.
Graham

Copy the greyscale file and paste it in the black channel of a new CMYK file

Or you can create a custum profile with Black Generation set to max